An Overview of Astrophysical Accelerators

There have been many acceleration mechanisms proposed to explain the presence of energetic charged particles that appear to fill the observable universe. All of these processes share an underlying similarity and they also appear to share a common upper energy limit that the charged particles are able to attain. I will discuss some of these mechanisms, several of which are presented at this conference session, and point out there similarities and argue that all of them are subject to the same scaling law that limits their maximum attainable energy (the Hillas rule).