diff --git a/pc/BUILD.gn b/pc/BUILD.gn
index 7e82c493e9..6e46301624 100644
--- a/pc/BUILD.gn
+++ b/pc/BUILD.gn
@@ -211,6 +211,7 @@ rtc_library("peerconnection") {
     ":jitter_buffer_delay",
     ":jitter_buffer_delay_interface",
     ":jitter_buffer_delay_proxy",
+    ":media_protocol_names",
     ":media_stream",
     ":peer_connection_message_handler",
     ":remote_audio_source",
@@ -230,22 +231,32 @@ rtc_library("peerconnection") {
     "../api:fec_controller_api",
     "../api:frame_transformer_interface",
     "../api:ice_transport_factory",
+    "../api:libjingle_logging_api",
     "../api:libjingle_peerconnection_api",
     "../api:media_stream_interface",
     "../api:network_state_predictor_api",
+    "../api:packet_socket_factory",
     "../api:priority",
     "../api:rtc_error",
     "../api:rtc_event_log_output_file",
     "../api:rtc_stats_api",
     "../api:rtp_parameters",
+    "../api:rtp_transceiver_direction",
     "../api:scoped_refptr",
+    "../api/adaptation:resource_adaptation_api",
     "../api/crypto:frame_decryptor_interface",
+    "../api/crypto:options",
     "../api/rtc_event_log",
     "../api/task_queue",
+    "../api/transport:bitrate_settings",
     "../api/transport:datagram_transport_interface",
+    "../api/transport:enums",
     "../api/transport:field_trial_based_config",
+    "../api/transport:webrtc_key_value_config",
     "../api/units:data_rate",
     "../api/video:builtin_video_bitrate_allocator_factory",
+    "../api/video:video_bitrate_allocator_factory",
+    "../api/video:video_codec_constants",
     "../api/video:video_frame",
     "../api/video:video_rtp_headers",
     "../api/video_codecs:video_codecs_api",
@@ -254,15 +265,19 @@ rtc_library("peerconnection") {
     "../logging:ice_log",
     "../media:rtc_data",
     "../media:rtc_media_base",
+    "../media:rtc_media_config",
     "../modules/rtp_rtcp:rtp_rtcp_format",
     "../p2p:rtc_p2p",
     "../rtc_base",
     "../rtc_base:checks",
+    "../rtc_base:deprecation",
+    "../rtc_base:robo_caller",
     "../rtc_base:rtc_base_approved",
     "../rtc_base:rtc_operations_chain",
     "../rtc_base:safe_minmax",
     "../rtc_base:weak_ptr",
     "../rtc_base/experiments:field_trial_parser",
+    "../rtc_base/network:sent_packet",
     "../rtc_base/synchronization:mutex",
     "../rtc_base/synchronization:sequence_checker",
     "../rtc_base/system:file_wrapper",
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index 3b090a28bf..e34a5be8b3 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -10,56 +10,50 @@
 
 #include "pc/peer_connection.h"
 
+#include <limits.h>
+#include <stddef.h>
 #include <algorithm>
-#include <limits>
-#include <memory>
-#include <queue>
-#include <set>
-#include <utility>
-#include <vector>
 
 #include "absl/algorithm/container.h"
 #include "absl/strings/match.h"
 #include "api/jsep_ice_candidate.h"
-#include "api/jsep_session_description.h"
-#include "api/media_stream_proxy.h"
-#include "api/media_stream_track_proxy.h"
-#include "api/rtc_error.h"
-#include "api/rtc_event_log/rtc_event_log.h"
-#include "api/rtc_event_log_output_file.h"
-#include "api/rtp_parameters.h"
+#include "api/rtp_transceiver_direction.h"
+#include "api/task_queue/queued_task.h"
+#include "api/transport/webrtc_key_value_config.h"
 #include "api/uma_metrics.h"
 #include "api/video/builtin_video_bitrate_allocator_factory.h"
-#include "call/call.h"
-#include "logging/rtc_event_log/ice_logger.h"
+#include "api/video/video_codec_constants.h"
+#include "call/audio_state.h"
+#include "call/packet_receiver.h"
+#include "media/base/media_config.h"
 #include "media/base/rid_description.h"
-#include "media/sctp/sctp_transport.h"
+#include "media/base/stream_params.h"
+#include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
+#include "p2p/base/connection.h"
+#include "p2p/base/connection_info.h"
+#include "p2p/base/dtls_transport_internal.h"
+#include "p2p/base/p2p_constants.h"
+#include "p2p/base/p2p_transport_channel.h"
+#include "p2p/base/transport_info.h"
 #include "pc/audio_rtp_receiver.h"
-#include "pc/audio_track.h"
-#include "pc/channel.h"
-#include "pc/channel_manager.h"
-#include "pc/dtmf_sender.h"
-#include "pc/media_stream.h"
-#include "pc/media_stream_observer.h"
-#include "pc/remote_audio_source.h"
-#include "pc/rtp_media_utils.h"
-#include "pc/rtp_receiver.h"
-#include "pc/rtp_sender.h"
+#include "pc/ice_server_parsing.h"
 #include "pc/sctp_transport.h"
-#include "pc/sctp_utils.h"
-#include "pc/sdp_offer_answer.h"
-#include "pc/sdp_utils.h"
-#include "pc/stream_collection.h"
+#include "pc/simulcast_description.h"
 #include "pc/video_rtp_receiver.h"
-#include "pc/video_track.h"
+#include "pc/webrtc_session_description_factory.h"
 #include "rtc_base/bind.h"
-#include "rtc_base/checks.h"
+#include "rtc_base/helpers.h"
+#include "rtc_base/ip_address.h"
+#include "rtc_base/location.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/net_helper.h"
+#include "rtc_base/network_constants.h"
+#include "rtc_base/robo_caller.h"
+#include "rtc_base/rtc_certificate_generator.h"
+#include "rtc_base/socket_address.h"
 #include "rtc_base/string_encode.h"
-#include "rtc_base/strings/string_builder.h"
 #include "rtc_base/task_utils/to_queued_task.h"
 #include "rtc_base/trace_event.h"
-#include "system_wrappers/include/clock.h"
 #include "system_wrappers/include/metrics.h"
 
 using cricket::ContentInfo;
diff --git a/pc/peer_connection.h b/pc/peer_connection.h
index 9949fcb8f0..c2ea92f055 100644
--- a/pc/peer_connection.h
+++ b/pc/peer_connection.h
@@ -11,6 +11,7 @@
 #ifndef PC_PEER_CONNECTION_H_
 #define PC_PEER_CONNECTION_H_
 
+#include <stdint.h>
 #include <functional>
 #include <map>
 #include <memory>
@@ -19,40 +20,84 @@
 #include <utility>
 #include <vector>
 
+#include "absl/types/optional.h"
+#include "api/adaptation/resource.h"
+#include "api/async_resolver_factory.h"
+#include "api/audio_options.h"
+#include "api/candidate.h"
+#include "api/crypto/crypto_options.h"
+#include "api/data_channel_interface.h"
+#include "api/dtls_transport_interface.h"
+#include "api/ice_transport_interface.h"
+#include "api/jsep.h"
+#include "api/media_stream_interface.h"
+#include "api/media_types.h"
+#include "api/packet_socket_factory.h"
 #include "api/peer_connection_interface.h"
+#include "api/rtc_error.h"
+#include "api/rtc_event_log/rtc_event_log.h"
+#include "api/rtc_event_log_output.h"
+#include "api/rtp_parameters.h"
+#include "api/rtp_receiver_interface.h"
+#include "api/rtp_sender_interface.h"
+#include "api/rtp_transceiver_interface.h"
+#include "api/scoped_refptr.h"
+#include "api/sctp_transport_interface.h"
+#include "api/set_local_description_observer_interface.h"
+#include "api/set_remote_description_observer_interface.h"
+#include "api/stats/rtc_stats_collector_callback.h"
+#include "api/transport/bitrate_settings.h"
 #include "api/transport/data_channel_transport_interface.h"
+#include "api/transport/enums.h"
 #include "api/turn_customizer.h"
+#include "api/video/video_bitrate_allocator_factory.h"
+#include "call/call.h"
+#include "media/base/media_channel.h"
+#include "media/base/media_engine.h"
+#include "p2p/base/ice_transport_internal.h"
+#include "p2p/base/port.h"
+#include "p2p/base/port_allocator.h"
+#include "p2p/base/transport_description.h"
+#include "pc/channel.h"
+#include "pc/channel_interface.h"
+#include "pc/channel_manager.h"
 #include "pc/connection_context.h"
 #include "pc/data_channel_controller.h"
-#include "pc/ice_server_parsing.h"
+#include "pc/data_channel_utils.h"
+#include "pc/dtls_transport.h"
 #include "pc/jsep_transport_controller.h"
-#include "pc/peer_connection_factory.h"
 #include "pc/peer_connection_internal.h"
 #include "pc/peer_connection_message_handler.h"
 #include "pc/rtc_stats_collector.h"
+#include "pc/rtp_data_channel.h"
+#include "pc/rtp_receiver.h"
 #include "pc/rtp_sender.h"
 #include "pc/rtp_transceiver.h"
-#include "pc/sctp_transport.h"
+#include "pc/rtp_transport_internal.h"
+#include "pc/sctp_data_channel.h"
 #include "pc/sdp_offer_answer.h"
+#include "pc/session_description.h"
 #include "pc/stats_collector.h"
 #include "pc/stream_collection.h"
 #include "pc/transceiver_list.h"
+#include "pc/transport_stats.h"
 #include "pc/usage_pattern.h"
-#include "pc/webrtc_session_description_factory.h"
-#include "rtc_base/experiments/field_trial_parser.h"
-#include "rtc_base/operations_chain.h"
-#include "rtc_base/race_checker.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/copy_on_write_buffer.h"
+#include "rtc_base/deprecation.h"
+#include "rtc_base/network/sent_packet.h"
+#include "rtc_base/rtc_certificate.h"
+#include "rtc_base/ssl_certificate.h"
+#include "rtc_base/ssl_stream_adapter.h"
+#include "rtc_base/synchronization/sequence_checker.h"
 #include "rtc_base/task_utils/pending_task_safety_flag.h"
+#include "rtc_base/third_party/sigslot/sigslot.h"
+#include "rtc_base/thread.h"
+#include "rtc_base/thread_annotations.h"
 #include "rtc_base/unique_id_generator.h"
-#include "rtc_base/weak_ptr.h"
 
 namespace webrtc {
 
-class MediaStreamObserver;
-class VideoRtpReceiver;
-class RtcEventLog;
-class SdpOfferAnswerHandler;
-
 // PeerConnection is the implementation of the PeerConnection object as defined
 // by the PeerConnectionInterface API surface.
 // The class currently is solely responsible for the following:
diff --git a/pc/sdp_offer_answer.cc b/pc/sdp_offer_answer.cc
index d03c29265d..29fdf3a797 100644
--- a/pc/sdp_offer_answer.cc
+++ b/pc/sdp_offer_answer.cc
@@ -11,16 +11,50 @@
 #include "pc/sdp_offer_answer.h"
 
 #include <algorithm>
+#include <iterator>
 #include <queue>
-#include <set>
+#include <type_traits>
 
+#include "absl/algorithm/container.h"
+#include "absl/strings/string_view.h"
+#include "api/array_view.h"
+#include "api/crypto/crypto_options.h"
+#include "api/data_channel_interface.h"
+#include "api/dtls_transport_interface.h"
 #include "api/media_stream_proxy.h"
+#include "api/rtp_parameters.h"
+#include "api/rtp_receiver_interface.h"
+#include "api/rtp_sender_interface.h"
 #include "api/uma_metrics.h"
+#include "media/base/codec.h"
+#include "media/base/media_engine.h"
+#include "media/base/rid_description.h"
+#include "p2p/base/p2p_constants.h"
+#include "p2p/base/p2p_transport_channel.h"
+#include "p2p/base/port.h"
+#include "p2p/base/transport_description.h"
+#include "p2p/base/transport_description_factory.h"
+#include "p2p/base/transport_info.h"
+#include "pc/data_channel_utils.h"
+#include "pc/media_protocol_names.h"
 #include "pc/media_stream.h"
-#include "pc/media_stream_observer.h"
 #include "pc/peer_connection.h"
 #include "pc/peer_connection_message_handler.h"
+#include "pc/rtp_data_channel.h"
 #include "pc/rtp_media_utils.h"
+#include "pc/rtp_transport_internal.h"
+#include "pc/simulcast_description.h"
+#include "pc/usage_pattern.h"
+#include "rtc_base/bind.h"
+#include "rtc_base/helpers.h"
+#include "rtc_base/location.h"
+#include "rtc_base/logging.h"
+#include "rtc_base/ref_counted_object.h"
+#include "rtc_base/socket_address.h"
+#include "rtc_base/ssl_stream_adapter.h"
+#include "rtc_base/string_encode.h"
+#include "rtc_base/strings/string_builder.h"
+#include "rtc_base/third_party/sigslot/sigslot.h"
 #include "rtc_base/trace_event.h"
 #include "system_wrappers/include/metrics.h"
 
diff --git a/pc/sdp_offer_answer.h b/pc/sdp_offer_answer.h
index 6483ef4b21..56f617505c 100644
--- a/pc/sdp_offer_answer.h
+++ b/pc/sdp_offer_answer.h
@@ -11,6 +11,9 @@
 #ifndef PC_SDP_OFFER_ANSWER_H_
 #define PC_SDP_OFFER_ANSWER_H_
 
+#include <stddef.h>
+#include <stdint.h>
+#include <functional>
 #include <map>
 #include <memory>
 #include <set>
@@ -18,25 +21,50 @@
 #include <utility>
 #include <vector>
 
+#include "absl/types/optional.h"
+#include "api/candidate.h"
+#include "api/jsep.h"
 #include "api/jsep_ice_candidate.h"
+#include "api/media_stream_interface.h"
+#include "api/media_types.h"
 #include "api/peer_connection_interface.h"
+#include "api/rtc_error.h"
+#include "api/rtp_transceiver_direction.h"
+#include "api/rtp_transceiver_interface.h"
+#include "api/scoped_refptr.h"
+#include "api/set_local_description_observer_interface.h"
+#include "api/set_remote_description_observer_interface.h"
 #include "api/transport/data_channel_transport_interface.h"
 #include "api/turn_customizer.h"
+#include "media/base/stream_params.h"
+#include "p2p/base/port_allocator.h"
+#include "pc/channel.h"
+#include "pc/channel_interface.h"
+#include "pc/channel_manager.h"
 #include "pc/data_channel_controller.h"
 #include "pc/ice_server_parsing.h"
 #include "pc/jsep_transport_controller.h"
+#include "pc/media_session.h"
+#include "pc/media_stream_observer.h"
 #include "pc/peer_connection_factory.h"
 #include "pc/peer_connection_internal.h"
 #include "pc/rtc_stats_collector.h"
+#include "pc/rtp_receiver.h"
 #include "pc/rtp_sender.h"
 #include "pc/rtp_transceiver.h"
 #include "pc/sctp_transport.h"
+#include "pc/session_description.h"
 #include "pc/stats_collector.h"
 #include "pc/stream_collection.h"
+#include "pc/transceiver_list.h"
 #include "pc/webrtc_session_description_factory.h"
+#include "rtc_base/checks.h"
 #include "rtc_base/experiments/field_trial_parser.h"
 #include "rtc_base/operations_chain.h"
 #include "rtc_base/race_checker.h"
+#include "rtc_base/synchronization/sequence_checker.h"
+#include "rtc_base/thread.h"
+#include "rtc_base/thread_annotations.h"
 #include "rtc_base/unique_id_generator.h"
 #include "rtc_base/weak_ptr.h"
 
@@ -156,8 +184,10 @@ class SdpOfferAnswerHandler {
 
  private:
   class ImplicitCreateSessionDescriptionObserver;
+
   friend class ImplicitCreateSessionDescriptionObserver;
   class SetSessionDescriptionObserverAdapter;
+
   friend class SetSessionDescriptionObserverAdapter;
 
   enum class SessionError {
diff --git a/tools_webrtc/iwyu/apply-iwyu b/tools_webrtc/iwyu/apply-iwyu
new file mode 100755
index 0000000000..a043493ad1
--- /dev/null
+++ b/tools_webrtc/iwyu/apply-iwyu
@@ -0,0 +1,35 @@
+#!/bin/sh
+#
+# Run the include-what-you-use tool (iwyu) on a file in the webrtc source
+# directory.
+#
+# The script uses a subsequent grep pass to remove #include files from .cc
+# that are also in the .h file, or are problematic to include.
+#
+# To get iwyu on Debian/glinux, do "sudo apt-get install iwyu".
+
+set -e
+set -x
+FILE=$1
+
+if [ ! -f $FILE.h ]; then
+   echo "$FILE.h not found"
+   exit 1
+fi
+
+if [ ! -f $FILE.cc ]; then
+   echo "$FILE.cc not found"
+   exit 1
+fi 
+
+iwyu -Xiwyu --no_fwd_decls --no-default-mappings -D__X86_64__  -DWEBRTC_POSIX -I . -I third_party/abseil-cpp $FILE.cc |& fix_include || echo "Some files modified"
+
+grep ^#include $FILE.h | grep -v -f - $FILE.cc > $FILE.ccnew
+grep -v -f tools_webrtc/iwyu/iwyu-filter-list $FILE.ccnew > $FILE.cc
+rm $FILE.ccnew
+grep -v -f tools_webrtc/iwyu/iwyu-filter-list $FILE.h > $FILE.hnew
+mv $FILE.hnew $FILE.h
+
+echo "Finished. Check diff, compile and git cl format before uploading."
+
+
diff --git a/tools_webrtc/iwyu/iwyu b/tools_webrtc/iwyu/iwyu
new file mode 100755
index 0000000000..7bbc69d496
--- /dev/null
+++ b/tools_webrtc/iwyu/iwyu
@@ -0,0 +1,11 @@
+#!/bin/bash
+#
+# Run IWYU against a single webrtc source file.
+#
+# To get iwyu on Debian/glinux, do "sudo apt-get install iwyu".
+#
+# To apply the changes suggested blindly, do tools/iwyu |& fix_include
+#
+# Doing "tools/iwyu filename.cc" will check both the .cc and .h file.
+# 
+iwyu -Xiwyu --no_fwd_decls -D__X86_64__  -DWEBRTC_POSIX -I . -I third_party/abseil-cpp $@
diff --git a/tools_webrtc/iwyu/iwyu-filter-list b/tools_webrtc/iwyu/iwyu-filter-list
new file mode 100644
index 0000000000..f31b996e91
--- /dev/null
+++ b/tools_webrtc/iwyu/iwyu-filter-list
@@ -0,0 +1,5 @@
+# These are lines that apply-iwyu will prevent from being added to a
+# file. They are lines that refer to files that are conditionally included
+# in certain configurations.
+#include <sys/socket.h>
+#include <ext/alloc_traits.h>