Exo-frames or E-frames for short were created by humans in their effort to terraform and colonize Venus and Mars and to protect themselves from any possible aggression from outside of the Solar System. They can be thus divided into two main categories — civilian and military models. However, since the series primarily described the Neosapien War that followed the Second Neosapien Revolt, nearly all E-frames shown in Exo-Squad were battle machines. Another distinction is that between human (Terran) and Neosapien E-frames.