diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
index 665fd6de4ed3..cae65b0604ff 100644
--- a/include/libcamera/internal/meson.build
+++ b/include/libcamera/internal/meson.build
@@ -34,6 +34,7 @@ libcamera_internal_headers = files([
     'pipeline_handler.h',
     'process.h',
     'pub_key.h',
+    'request.h',
     'source_paths.h',
     'sysfs.h',
     'v4l2_device.h',
diff --git a/include/libcamera/internal/request.h b/include/libcamera/internal/request.h
new file mode 100644
index 000000000000..630ae60e8b6c
--- /dev/null
+++ b/include/libcamera/internal/request.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Google Inc.
+ *
+ * request.h - Internal capture request handling
+ */
+#ifndef __LIBCAMERA_INTERNAL_REQUEST_H__
+#define __LIBCAMERA_INTERNAL_REQUEST_H__
+
+#include <unordered_set>
+
+#include <libcamera/base/class.h>
+
+#include <libcamera/request.h>
+
+namespace libcamera {
+
+class Camera;
+class CameraControlValidator;
+class FrameBuffer;
+
+class Request::Private : public Extensible::Private
+{
+	LIBCAMERA_DECLARE_PUBLIC(Request)
+
+private:
+	std::unordered_set<FrameBuffer *> pending_;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_INTERNAL_REQUEST_H__ */
diff --git a/include/libcamera/request.h b/include/libcamera/request.h
index 2d361c9d97dc..71d088551d94 100644
--- a/include/libcamera/request.h
+++ b/include/libcamera/request.h
@@ -25,8 +25,10 @@ class CameraControlValidator;
 class FrameBuffer;
 class Stream;
 
-class Request
+class Request : public Extensible
 {
+	LIBCAMERA_DECLARE_PRIVATE()
+
 public:
 	enum Status {
 		RequestPending,
@@ -56,7 +58,7 @@ public:
 	uint64_t cookie() const { return cookie_; }
 	Status status() const { return status_; }
 
-	bool hasPendingBuffers() const { return !pending_.empty(); }
+	bool hasPendingBuffers() const;
 
 	std::string toString() const;
 
@@ -75,7 +77,6 @@ private:
 	ControlList *controls_;
 	ControlList *metadata_;
 	BufferMap bufferMap_;
-	std::unordered_set<FrameBuffer *> pending_;
 
 	uint32_t sequence_;
 	const uint64_t cookie_;
diff --git a/src/libcamera/request.cpp b/src/libcamera/request.cpp
index f95ce4db5eaa..d363d7a7b005 100644
--- a/src/libcamera/request.cpp
+++ b/src/libcamera/request.cpp
@@ -5,7 +5,7 @@
  * request.cpp - Capture request handling
  */
 
-#include <libcamera/request.h>
+#include "libcamera/internal/request.h"
 
 #include <map>
 #include <sstream>
@@ -22,14 +22,26 @@
 #include "libcamera/internal/tracepoints.h"
 
 /**
- * \file request.h
+ * \file libcamera/request.h
  * \brief Describes a frame capture request to be processed by a camera
+ *
+ * \file internal/request.h
+ * \brief Provides the internal implementation details for a Request
  */
 
 namespace libcamera {
 
 LOG_DEFINE_CATEGORY(Request)
 
+/**
+ * \class Request::Private
+ * \brief Base class for FrameBuffer private data
+ *
+ * The Request::Private class stores all private data associated with a request.
+ * It implements the d-pointer design pattern to hide core Request data from the
+ * public API, and exposes utility functions to pipeline handlers.
+ */
+
 /**
  * \enum Request::Status
  * Request completion status
@@ -74,8 +86,9 @@ LOG_DEFINE_CATEGORY(Request)
  * completely opaque to libcamera.
  */
 Request::Request(Camera *camera, uint64_t cookie)
-	: camera_(camera), sequence_(0), cookie_(cookie),
-	  status_(RequestPending), cancelled_(false)
+	: Extensible(std::make_unique<Private>()), camera_(camera),
+	  sequence_(0), cookie_(cookie), status_(RequestPending),
+	  cancelled_(false)
 {
 	/**
 	 * \todo Should the Camera expose a validator instance, to avoid
@@ -117,12 +130,11 @@ void Request::reuse(ReuseFlag flags)
 {
 	LIBCAMERA_TRACEPOINT(request_reuse, this);
 
-	pending_.clear();
+	_d()->pending_.clear();
 	if (flags & ReuseBuffers) {
 		for (auto pair : bufferMap_) {
 			FrameBuffer *buffer = pair.second;
 			buffer->_d()->setRequest(this);
-			pending_.insert(buffer);
 		}
 	} else {
 		bufferMap_.clear();
@@ -192,7 +204,7 @@ int Request::addBuffer(const Stream *stream, FrameBuffer *buffer)
 	}
 
 	buffer->_d()->setRequest(this);
-	pending_.insert(buffer);
+	_d()->pending_.insert(buffer);
 	bufferMap_[stream] = buffer;
 
 	return 0;
@@ -267,12 +279,15 @@ FrameBuffer *Request::findBuffer(const Stream *stream) const
  */
 
 /**
- * \fn Request::hasPendingBuffers()
  * \brief Check if a request has buffers yet to be completed
  *
  * \return True if the request has buffers pending for completion, false
  * otherwise
  */
+bool Request::hasPendingBuffers() const
+{
+	return !_d()->pending_.empty();
+}
 
 /**
  * \brief Complete a queued request
@@ -307,12 +322,12 @@ void Request::cancel()
 
 	ASSERT(status_ == RequestPending);
 
-	for (FrameBuffer *buffer : pending_) {
+	for (FrameBuffer *buffer : _d()->pending_) {
 		buffer->cancel();
 		camera_->bufferCompleted.emit(this, buffer);
 	}
 
-	pending_.clear();
+	_d()->pending_.clear();
 	cancelled_ = true;
 }
 
@@ -333,7 +348,7 @@ bool Request::completeBuffer(FrameBuffer *buffer)
 {
 	LIBCAMERA_TRACEPOINT(request_complete_buffer, this, buffer);
 
-	int ret = pending_.erase(buffer);
+	int ret = _d()->pending_.erase(buffer);
 	ASSERT(ret == 1);
 
 	buffer->_d()->setRequest(nullptr);
@@ -361,7 +376,7 @@ std::string Request::toString() const
 
 	/* Example Output: Request(55:P:1/2:6523524) */
 	ss << "Request(" << sequence_ << ":" << statuses[status_] << ":"
-	   << pending_.size() << "/" << bufferMap_.size() << ":"
+	   << _d()->pending_.size() << "/" << bufferMap_.size() << ":"
 	   << cookie_ << ")";
 
 	return ss.str();