  Autonomous systems are highly complex and present unique challenges for the
application of formal methods. Autonomous systems act without human
intervention, and are often embedded in a robotic system, so that they can
interact with the real world. As such, they exhibit the properties of
safety-critical, cyber-physical, hybrid, and real-time systems.
  This EPTCS volume contains the proceedings for the third workshop on Formal
Methods for Autonomous Systems (FMAS 2021), which was held virtually on the
21st and 22nd of October 2021. Like the previous workshop, FMAS 2021 was an
online, stand-alone event, as an adaptation to the ongoing COVID-19
restrictions. Despite the challenges this brought, we were determined to build
on the success of the previous two FMAS workshops.
  The goal of FMAS is to bring together leading researchers who are tackling
the unique challenges of autonomous systems using formal methods, to present
recent and ongoing work. We are interested in the use of formal methods to
specify, model, or verify autonomous and/or robotic systems; in whole or in
part. We are also interested in successful industrial applications and
potential future directions for this emerging application of formal methods.
