This chapter discusses the concept of swarms of autonomous robotic platforms in the underwater environment. The submarine domain is made particularly complex to operate in by the high level of absorption of radio waves by water. There are thus large effects on navigation and communication, two things that are essential for effective autonomous swarms. Autonomous underwater vehicles (AUVs) and their origins are introduced, along with some definitions of the descriptions of various swarming configurations. The challenges of operations in the marine environment are explored for their impact on swarm dynamics and function. The systems that show potential in the land, air and space domains are not necessarily applicable underwater. Although AUVs are already seeing deployment for surveying tasks in oceans, lakes and rivers around the world, collaborative autonomy is a modality that suffers from low-bandwidth and high-latency communication, degraded positional information and extremely limited situational awareness. Not all of the challenges in the development of autonomous swarms are the consequence of the physical environment. Swarm developers and owners have different priorities and perspectives. The chapter addresses the need for stakeholders to understand each other and proposes a mechanism for communicating mission needs and design considerations.