We asked our contributors to share their favorite photos that show pairs and companions, or two of a kind, and they returned with a range of macro to wide-angle shots, featuring a variety of marine life large and small from around the world.

This article is an abridged version of an early chapter in Simon Pridmore’s history of the early days of technical diving, Technically Speaking—Talks on Technical Diving, Volume 1: Genesis and Exodus. The nitrox saga would end up as the subject of vitriolic debate and bitter division in the sport diving community for half a decade. This is its origin story.