diff --git a/cpp/include/cudf/scalar/scalar.hpp b/cpp/include/cudf/scalar/scalar.hpp
index 0db729aec28..24c356f1fd7 100644
--- a/cpp/include/cudf/scalar/scalar.hpp
+++ b/cpp/include/cudf/scalar/scalar.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2021, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2022, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,6 +51,8 @@ class scalar {
 
   /**
    * @brief Returns the scalar's logical value type.
+   *
+   * @return The scalar's logical value type
    */
   [[nodiscard]] data_type type() const noexcept;
 
@@ -69,18 +71,22 @@ class scalar {
    * function does a stream synchronization.
    *
    * @param stream CUDA stream used for device memory operations.
-   * @return true Value is valid.
-   * @return false Value is invalid/null.
+   * @return true Value is valid
+   * @return false Value is invalid/null
    */
   [[nodiscard]] bool is_valid(rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
 
   /**
    * @brief Returns a raw pointer to the validity bool in device memory.
+   *
+   * @return Raw pointer to the validity bool in device memory
    */
   bool* validity_data();
 
   /**
-   * @brief Returns a const raw pointer to the validity bool in device memory.
+   * @brief Return a const raw pointer to the validity bool in device memory.
+   *
+   * @return Raw pointer to the validity bool in device memory
    */
   [[nodiscard]] bool const* validity_data() const;
 
@@ -90,6 +96,10 @@ class scalar {
 
   scalar() = delete;
 
+  /**
+   * @brief Move constructor for scalar.
+   * @param other The other scalar to move from.
+   */
   scalar(scalar&& other) = default;
 
   /**
@@ -121,14 +131,24 @@ class scalar {
 };
 
 namespace detail {
+/**
+ * @brief An owning class to represent a fixed-width type value in device memory.
+ *
+ * @tparam T the data type of the fixed-width type value.
+ */
 template <typename T>
 class fixed_width_scalar : public scalar {
   static_assert(is_fixed_width<T>(), "Unexpected non-fixed-width type.");
 
  public:
-  using value_type = T;
+  using value_type = T;  ///< Type of the value held by the scalar.
+
+  ~fixed_width_scalar() override = default;
 
-  ~fixed_width_scalar() override                 = default;
+  /**
+   * @brief Move constructor for fixed_width_scalar.
+   * @param other The other fixed_width_scalar to move from.
+   */
   fixed_width_scalar(fixed_width_scalar&& other) = default;
 
   fixed_width_scalar& operator=(fixed_width_scalar const& other) = delete;
@@ -162,16 +182,19 @@ class fixed_width_scalar : public scalar {
    * @brief Get the value of the scalar.
    *
    * @param stream CUDA stream used for device memory operations.
+   * @return Value of the scalar
    */
   T value(rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
 
   /**
    * @brief Returns a raw pointer to the value in device memory.
+   * @return A raw pointer to the value in device memory
    */
   T* data();
 
   /**
    * @brief Returns a const raw pointer to the value in device memory.
+   * @return A const raw pointer to the value in device memory
    */
   T const* data() const;
 
@@ -219,8 +242,13 @@ class numeric_scalar : public detail::fixed_width_scalar<T> {
   static_assert(is_numeric<T>(), "Unexpected non-numeric type.");
 
  public:
-  numeric_scalar()                       = delete;
-  ~numeric_scalar()                      = default;
+  numeric_scalar()  = delete;
+  ~numeric_scalar() = default;
+
+  /**
+   * @brief Move constructor for numeric_scalar.
+   * @param other The other numeric_scalar to move from.
+   */
   numeric_scalar(numeric_scalar&& other) = default;
 
   numeric_scalar& operator=(numeric_scalar const& other) = delete;
@@ -274,11 +302,16 @@ class fixed_point_scalar : public scalar {
   static_assert(is_fixed_point<T>(), "Unexpected non-fixed_point type.");
 
  public:
-  using rep_type   = typename T::rep;
-  using value_type = T;
+  using rep_type   = typename T::rep;  ///< The representation type of the fixed_point number.
+  using value_type = T;                ///< The value type of the fixed_point number.
+
+  fixed_point_scalar()           = delete;
+  ~fixed_point_scalar() override = default;
 
-  fixed_point_scalar()                           = delete;
-  ~fixed_point_scalar() override                 = default;
+  /**
+   * @brief Move constructor for fixed_point_scalar.
+   * @param other The other fixed_point_scalar to move from.
+   */
   fixed_point_scalar(fixed_point_scalar&& other) = default;
 
   fixed_point_scalar& operator=(fixed_point_scalar const& other) = delete;
@@ -355,6 +388,7 @@ class fixed_point_scalar : public scalar {
    * @brief Get the value of the scalar.
    *
    * @param stream CUDA stream used for device memory operations.
+   * @return The value of the scalar
    */
   rep_type value(rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
 
@@ -362,6 +396,7 @@ class fixed_point_scalar : public scalar {
    * @brief Get the decimal32, decimal64 or decimal128.
    *
    * @param stream CUDA stream used for device memory operations.
+   * @return The decimal32, decimal64 or decimal128 value
    */
   T fixed_point_value(rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
 
@@ -372,11 +407,13 @@ class fixed_point_scalar : public scalar {
 
   /**
    * @brief Returns a raw pointer to the value in device memory.
+   * @return A raw pointer to the value in device memory
    */
   rep_type* data();
 
   /**
    * @brief Returns a const raw pointer to the value in device memory.
+   * @return a const raw pointer to the value in device memory
    */
   rep_type const* data() const;
 
@@ -389,10 +426,15 @@ class fixed_point_scalar : public scalar {
  */
 class string_scalar : public scalar {
  public:
-  using value_type = cudf::string_view;
+  using value_type = cudf::string_view;  ///< The value type of the string scalar.
+
+  string_scalar()           = delete;
+  ~string_scalar() override = default;
 
-  string_scalar()                      = delete;
-  ~string_scalar() override            = default;
+  /**
+   * @brief Move constructor for string_scalar.
+   * @param other The other string_scalar to move from.
+   */
   string_scalar(string_scalar&& other) = default;
 
   // string_scalar(string_scalar const& other) = delete;
@@ -478,6 +520,7 @@ class string_scalar : public scalar {
    * @brief Get the value of the scalar in a host std::string.
    *
    * @param stream CUDA stream used for device memory operations.
+   * @return The value of the scalar in a host std::string
    */
   [[nodiscard]] std::string to_string(
     rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
@@ -486,16 +529,19 @@ class string_scalar : public scalar {
    * @brief Get the value of the scalar as a string_view.
    *
    * @param stream CUDA stream used for device memory operations.
+   * @return The value of the scalar as a string_view
    */
   [[nodiscard]] value_type value(rmm::cuda_stream_view stream = rmm::cuda_stream_default) const;
 
   /**
    * @brief Returns the size of the string in bytes.
+   * @return The size of the string in bytes
    */
   [[nodiscard]] size_type size() const;
 
   /**
    * @brief Returns a raw pointer to the string in device memory.
+   * @return a raw pointer to the string in device memory
    */
   [[nodiscard]] const char* data() const;
 
@@ -514,8 +560,13 @@ class chrono_scalar : public detail::fixed_width_scalar<T> {
   static_assert(is_chrono<T>(), "Unexpected non-chrono type");
 
  public:
-  chrono_scalar()                      = delete;
-  ~chrono_scalar()                     = default;
+  chrono_scalar()  = delete;
+  ~chrono_scalar() = default;
+
+  /**
+   * @brief Move constructor for chrono_scalar.
+   * @param other The other chrono_scalar to move from.
+   */
   chrono_scalar(chrono_scalar&& other) = default;
 
   chrono_scalar& operator=(chrono_scalar const& other) = delete;
@@ -559,14 +610,25 @@ class chrono_scalar : public detail::fixed_width_scalar<T> {
                 rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 };
 
+/**
+ * @brief An owning class to represent a timestamp value in device memory.
+ *
+ * @tparam T the data type of the timestamp value.
+ * @see cudf/wrappers/timestamps.hpp for a list of allowed types.
+ */
 template <typename T>
 class timestamp_scalar : public chrono_scalar<T> {
  public:
   static_assert(is_timestamp<T>(), "Unexpected non-timestamp type");
   using chrono_scalar<T>::chrono_scalar;
-  using rep_type = typename T::rep;
+  using rep_type = typename T::rep;  ///< The underlying representation type of the timestamp.
+
+  timestamp_scalar() = delete;
 
-  timestamp_scalar()                         = delete;
+  /**
+   * @brief Move constructor for timestamp_scalar.
+   * @param other The other timestamp_scalar to move from.
+   */
   timestamp_scalar(timestamp_scalar&& other) = default;
 
   /**
@@ -597,19 +659,31 @@ class timestamp_scalar : public chrono_scalar<T> {
                    rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
   /**
-   * @brief Return the duration in number of ticks since the UNIX epoch.
+   * @brief Returns the duration in number of ticks since the UNIX epoch.
+   * @return The duration in number of ticks since the UNIX epoch
    */
   rep_type ticks_since_epoch();
 };
 
+/**
+ * @brief An owning class to represent a duration value in device memory.
+ *
+ * @tparam T the data type of the duration value.
+ * @see cudf/wrappers/durations.hpp for a list of allowed types.
+ */
 template <typename T>
 class duration_scalar : public chrono_scalar<T> {
  public:
   static_assert(is_duration<T>(), "Unexpected non-duration type");
   using chrono_scalar<T>::chrono_scalar;
-  using rep_type = typename T::rep;
+  using rep_type = typename T::rep;  ///< The duration's underlying representation type.
+
+  duration_scalar() = delete;
 
-  duration_scalar()                        = delete;
+  /**
+   * @brief Move constructor for duration_scalar.
+   * @param other The other duration_scalar to move from.
+   */
   duration_scalar(duration_scalar&& other) = default;
 
   /**
@@ -637,7 +711,8 @@ class duration_scalar : public chrono_scalar<T> {
                   rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
   /**
-   * @brief Return the duration in number of ticks.
+   * @brief Returns the duration in number of ticks.
+   * @return The duration in number of ticks
    */
   rep_type count();
 };
@@ -647,8 +722,13 @@ class duration_scalar : public chrono_scalar<T> {
  */
 class list_scalar : public scalar {
  public:
-  list_scalar()                    = delete;
-  ~list_scalar() override          = default;
+  list_scalar()           = delete;
+  ~list_scalar() override = default;
+
+  /**
+   * @brief Move constructor for list_scalar.
+   * @param other The other list_scalar to move from.
+   */
   list_scalar(list_scalar&& other) = default;
 
   list_scalar& operator=(list_scalar const& other) = delete;
@@ -695,6 +775,7 @@ class list_scalar : public scalar {
 
   /**
    * @brief Returns a non-owning, immutable view to underlying device data.
+   * @return A non-owning, immutable view to underlying device data
    */
   [[nodiscard]] column_view view() const;
 
@@ -707,12 +788,24 @@ class list_scalar : public scalar {
  */
 class struct_scalar : public scalar {
  public:
-  struct_scalar()                      = delete;
-  ~struct_scalar() override            = default;
+  struct_scalar()           = delete;
+  ~struct_scalar() override = default;
+
+  /**
+   * @brief Move constructor for struct_scalar.
+   * @param other The other struct_scalar to move from.
+   */
   struct_scalar(struct_scalar&& other) = default;
   struct_scalar& operator=(struct_scalar const& other) = delete;
   struct_scalar& operator=(struct_scalar&& other) = delete;
 
+  /**
+   * @brief Construct a new struct scalar object by deep copying another.
+   *
+   * @param other The scalar to copy.
+   * @param stream CUDA stream used for device memory operations.
+   * @param mr Device memory resource to use for device memory allocation.
+   */
   struct_scalar(struct_scalar const& other,
                 rmm::cuda_stream_view stream        = rmm::cuda_stream_default,
                 rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
@@ -765,6 +858,7 @@ class struct_scalar : public scalar {
 
   /**
    * @brief Returns a non-owning, immutable view to underlying device data.
+   * @return A non-owning, immutable view to underlying device data
    */
   [[nodiscard]] table_view view() const;
 
diff --git a/cpp/include/cudf/scalar/scalar_device_view.cuh b/cpp/include/cudf/scalar/scalar_device_view.cuh
index ae658da9f9b..b298b462a4f 100644
--- a/cpp/include/cudf/scalar/scalar_device_view.cuh
+++ b/cpp/include/cudf/scalar/scalar_device_view.cuh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2021, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2022, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -36,6 +36,7 @@ class scalar_device_view_base {
 
   /**
    * @brief Returns the value type
+   * @returns The value type
    */
   [[nodiscard]] __host__ __device__ data_type type() const noexcept { return _type; }
 
@@ -59,6 +60,14 @@ class scalar_device_view_base {
   bool* _is_valid{};                ///< Pointer to device memory containing
                                     ///< boolean representing validity of the value.
 
+  /**
+   * @brief Construct a new scalar device view base object  from a device pointer
+   * and a validity boolean.
+   *
+   * @param type The data type of the scalar
+   * @param is_valid Pointer to device memory containing boolean representing
+   * validity of the scalar.
+   */
   scalar_device_view_base(data_type type, bool* is_valid) : _type(type), _is_valid(is_valid) {}
 
   scalar_device_view_base() = default;
@@ -73,6 +82,7 @@ class fixed_width_scalar_device_view_base : public detail::scalar_device_view_ba
    * @brief Returns reference to stored value.
    *
    * @tparam T The desired type
+   * @returns Reference to stored value
    */
   template <typename T>
   __device__ T& value() noexcept
@@ -84,6 +94,7 @@ class fixed_width_scalar_device_view_base : public detail::scalar_device_view_ba
    * @brief Returns const reference to stored value.
    *
    * @tparam T The desired type
+   * @returns Const reference to stored value
    */
   template <typename T>
   __device__ T const& value() const noexcept
@@ -107,16 +118,19 @@ class fixed_width_scalar_device_view_base : public detail::scalar_device_view_ba
    * @brief Returns a raw pointer to the value in device memory
    *
    * @tparam T The desired type
+   * @returns Raw pointer to the value in device memory
    */
   template <typename T>
   __device__ T* data() noexcept
   {
     return static_cast<T*>(_data);
   }
+
   /**
    * @brief Returns a const raw pointer to the value in device memory
    *
    * @tparam T The desired type
+   * @returns Const raw pointer to the value in device memory
    */
   template <typename T>
   __device__ T const* data() const noexcept
@@ -150,15 +164,19 @@ class fixed_width_scalar_device_view_base : public detail::scalar_device_view_ba
 template <typename T>
 class fixed_width_scalar_device_view : public detail::fixed_width_scalar_device_view_base {
  public:
-  using value_type = T;
+  using value_type = T;  ///< The value type of the scalar
 
   /**
    * @brief Returns reference to stored value.
+   *
+   * @returns Reference to stored value
    */
   __device__ T& value() noexcept { return fixed_width_scalar_device_view_base::value<T>(); }
 
   /**
    * @brief Returns const reference to stored value.
+   *
+   * @returns Const reference to stored value
    */
   __device__ T const& value() const noexcept
   {
@@ -174,10 +192,15 @@ class fixed_width_scalar_device_view : public detail::fixed_width_scalar_device_
 
   /**
    * @brief Returns a raw pointer to the value in device memory
+   *
+   * @returns Raw pointer to the value in device memory
    */
   __device__ T* data() noexcept { return fixed_width_scalar_device_view_base::data<T>(); }
+
   /**
    * @brief Returns a const raw pointer to the value in device memory
+   *
+   * @returns Const raw pointer to the value in device memory
    */
   __device__ T const* data() const noexcept
   {
@@ -210,6 +233,14 @@ class fixed_width_scalar_device_view : public detail::fixed_width_scalar_device_
 template <typename T>
 class numeric_scalar_device_view : public detail::fixed_width_scalar_device_view<T> {
  public:
+  /**
+   * @brief Construct a new numeric scalar device view object from data and validity pointers.
+   *
+   * @param type The data type of the value
+   * @param data The pointer to the data in device memory
+   * @param is_valid The pointer to the bool in device memory that indicates the
+   * validity of the stored value
+   */
   numeric_scalar_device_view(data_type type, T* data, bool* is_valid)
     : detail::fixed_width_scalar_device_view<T>(type, data, is_valid)
   {
@@ -222,8 +253,16 @@ class numeric_scalar_device_view : public detail::fixed_width_scalar_device_view
 template <typename T>
 class fixed_point_scalar_device_view : public detail::scalar_device_view_base {
  public:
-  using rep_type = typename T::rep;
+  using rep_type = typename T::rep;  ///< The representation type of the fixed_point value
 
+  /**
+   * @brief Construct a new fixed point scalar device view object from data and validity pointers.
+   *
+   * @param type The data type of the value
+   * @param data The pointer to the data in device memory
+   * @param is_valid The pointer to the bool in device memory that indicates the
+   * validity of the stored value
+   */
   fixed_point_scalar_device_view(data_type type, rep_type* data, bool* is_valid)
     : detail::scalar_device_view_base(type, is_valid), _data(data)
   {
@@ -238,6 +277,8 @@ class fixed_point_scalar_device_view : public detail::scalar_device_view_base {
 
   /**
    * @brief Get the value of the scalar, as a `rep_type`.
+   *
+   * @returns The value of the scalar, as a `rep_type`
    */
   __device__ rep_type const& rep() const noexcept { return *_data; }
 
@@ -250,8 +291,18 @@ class fixed_point_scalar_device_view : public detail::scalar_device_view_base {
  */
 class string_scalar_device_view : public detail::scalar_device_view_base {
  public:
-  using ValueType = cudf::string_view;
+  using ValueType = cudf::string_view;  ///< The value type of the string scalar
 
+  /**
+   * @brief Construct a new string scalar device view object from string data, size and validity
+   * pointers.
+   *
+   * @param type The data type of the value
+   * @param data The pointer to the string data in device memory
+   * @param is_valid The pointer to the bool in device memory that indicates the
+   * validity of the stored value
+   * @param size The pointer to the size of the string in device memory
+   */
   string_scalar_device_view(data_type type, const char* data, bool* is_valid, size_type size)
     : detail::scalar_device_view_base(type, is_valid), _data(data), _size(size)
   {
@@ -259,6 +310,8 @@ class string_scalar_device_view : public detail::scalar_device_view_base {
 
   /**
    * @brief Returns string_view of the value of this scalar.
+   *
+   * @returns string_view of the value of this scalar
    */
   [[nodiscard]] __device__ ValueType value() const noexcept
   {
@@ -267,6 +320,8 @@ class string_scalar_device_view : public detail::scalar_device_view_base {
 
   /**
    * @brief Returns a raw pointer to the value in device memory
+   *
+   * @returns Raw pointer to the value in device memory
    */
   [[nodiscard]] __device__ char const* data() const noexcept
   {
@@ -275,6 +330,8 @@ class string_scalar_device_view : public detail::scalar_device_view_base {
 
   /**
    * @brief Returns the size of the string in bytes.
+   *
+   * @returns The size of the string in bytes
    */
   [[nodiscard]] __device__ size_type size() const noexcept { return _size; }
 
@@ -289,6 +346,14 @@ class string_scalar_device_view : public detail::scalar_device_view_base {
 template <typename T>
 class timestamp_scalar_device_view : public detail::fixed_width_scalar_device_view<T> {
  public:
+  /**
+   * @brief Construct a new timestamp scalar device view object
+   *
+   * @param type The data type of the value
+   * @param data The pointer to the data in device memory
+   * @param is_valid The pointer to the bool in device memory that indicates the
+   * validity of the stored value
+   */
   timestamp_scalar_device_view(data_type type, T* data, bool* is_valid)
     : detail::fixed_width_scalar_device_view<T>(type, data, is_valid)
   {
@@ -301,6 +366,14 @@ class timestamp_scalar_device_view : public detail::fixed_width_scalar_device_vi
 template <typename T>
 class duration_scalar_device_view : public detail::fixed_width_scalar_device_view<T> {
  public:
+  /**
+   * @brief Construct a new duration scalar device view object from data and validity pointers.
+   *
+   * @param type The data type of the value
+   * @param data The pointer to the data in device memory
+   * @param is_valid The pointer to the bool in device memory that indicates the
+   * validity of the stored value
+   */
   duration_scalar_device_view(data_type type, T* data, bool* is_valid)
     : detail::fixed_width_scalar_device_view<T>(type, data, is_valid)
   {
@@ -309,6 +382,9 @@ class duration_scalar_device_view : public detail::fixed_width_scalar_device_vie
 
 /**
  * @brief Get the device view of a numeric_scalar
+ *
+ * @param s The numeric_scalar to get the device view of
+ * @return A device view of a numeric_scalar
  */
 template <typename T>
 auto get_scalar_device_view(numeric_scalar<T>& s)
@@ -318,6 +394,9 @@ auto get_scalar_device_view(numeric_scalar<T>& s)
 
 /**
  * @brief Get the device view of a string_scalar
+ *
+ * @param s The string_scalar to get the device view of
+ * @return A device view of a string_scalar
  */
 inline auto get_scalar_device_view(string_scalar& s)
 {
@@ -326,6 +405,9 @@ inline auto get_scalar_device_view(string_scalar& s)
 
 /**
  * @brief Get the device view of a timestamp_scalar
+ *
+ * @param s The timestamp_scalar to get the device view of
+ * @return A device view of a timestamp_scalar
  */
 template <typename T>
 auto get_scalar_device_view(timestamp_scalar<T>& s)
@@ -335,6 +417,9 @@ auto get_scalar_device_view(timestamp_scalar<T>& s)
 
 /**
  * @brief Get the device view of a duration_scalar
+ *
+ * @param s The duration_scalar to get the device view of
+ * @return A device view of a duration_scalar
  */
 template <typename T>
 auto get_scalar_device_view(duration_scalar<T>& s)
@@ -344,6 +429,9 @@ auto get_scalar_device_view(duration_scalar<T>& s)
 
 /**
  * @brief Get the device view of a fixed_point_scalar
+ *
+ * @param s The fixed_point_scalar to get the device view of
+ * @return The device view of the fixed_point_scalar
  */
 template <typename T>
 auto get_scalar_device_view(fixed_point_scalar<T>& s)
diff --git a/cpp/include/cudf/scalar/scalar_factories.hpp b/cpp/include/cudf/scalar/scalar_factories.hpp
index aa63fa7ffd4..305732d6b0b 100644
--- a/cpp/include/cudf/scalar/scalar_factories.hpp
+++ b/cpp/include/cudf/scalar/scalar_factories.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2021, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2022, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,6 +37,7 @@ namespace cudf {
  * @param type The desired numeric element type
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns An uninitialized numeric scalar
  */
 std::unique_ptr<scalar> make_numeric_scalar(
   data_type type,
@@ -53,6 +54,7 @@ std::unique_ptr<scalar> make_numeric_scalar(
  * @param type The desired timestamp element type
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @return An uninitialized timestamp scalar
  */
 std::unique_ptr<scalar> make_timestamp_scalar(
   data_type type,
@@ -69,6 +71,7 @@ std::unique_ptr<scalar> make_timestamp_scalar(
  * @param type The desired duration element type
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @return An uninitialized duration scalar
  */
 std::unique_ptr<scalar> make_duration_scalar(
   data_type type,
@@ -85,6 +88,7 @@ std::unique_ptr<scalar> make_duration_scalar(
  * @param type The desired fixed-width element type
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @return An uninitialized fixed-width scalar
  */
 std::unique_ptr<scalar> make_fixed_width_scalar(
   data_type type,
@@ -101,6 +105,7 @@ std::unique_ptr<scalar> make_fixed_width_scalar(
  * @param string The `std::string` to copy to device
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A string scalar with the contents of `string`
  */
 std::unique_ptr<scalar> make_string_scalar(
   std::string const& string,
@@ -115,6 +120,7 @@ std::unique_ptr<scalar> make_string_scalar(
  * @param type The desired element type
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A scalar of type `type`
  */
 std::unique_ptr<scalar> make_default_constructed_scalar(
   data_type type,
@@ -129,6 +135,7 @@ std::unique_ptr<scalar> make_default_constructed_scalar(
  * @param input Immutable view of input column to emulate
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A scalar of type of `input` column
  */
 std::unique_ptr<scalar> make_empty_scalar_like(
   column_view const& input,
@@ -142,6 +149,7 @@ std::unique_ptr<scalar> make_empty_scalar_like(
  * @param value The value to store in the scalar object
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A scalar of type `T`
  */
 template <typename T>
 std::unique_ptr<scalar> make_fixed_width_scalar(
@@ -160,6 +168,7 @@ std::unique_ptr<scalar> make_fixed_width_scalar(
  * @param scale The scale of the fixed point value
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A scalar of type `T`
  */
 template <typename T>
 std::unique_ptr<scalar> make_fixed_point_scalar(
@@ -177,6 +186,7 @@ std::unique_ptr<scalar> make_fixed_point_scalar(
  * @param elements Elements of the list
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A list scalar
  */
 std::unique_ptr<scalar> make_list_scalar(
   column_view elements,
@@ -191,6 +201,7 @@ std::unique_ptr<scalar> make_list_scalar(
  * @param data The columnar data to store in the scalar object
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A struct scalar
  */
 std::unique_ptr<scalar> make_struct_scalar(
   table_view const& data,
@@ -205,6 +216,7 @@ std::unique_ptr<scalar> make_struct_scalar(
  * @param data The columnar data to store in the scalar object
  * @param stream CUDA stream used for device memory operations.
  * @param mr Device memory resource used to allocate the scalar's `data` and `is_valid` bool.
+ * @returns A struct scalar
  */
 std::unique_ptr<scalar> make_struct_scalar(
   host_span<column_view const> data,