The purpose of RF4 is to advance and consolidate the diving community’s knowledge of rebreather technology and its use by technical, government and scientific divers, with the goal of improving rebreather diving safety and performance. The core of the event is a three-day scientific meeting organized by Drs. John Clarke, Simon Mitchell, Neal Pollock, and Frauke Tillmans, and journalist Michael Menduno, that will focus on diving safety, physiology, technology, training and operations. Proceedings will be published after the event that captures both presentation and discussion. made publicly available. Broadcast-quality videos of presentations will also be made available.