The successful integration and acceptance of many multi-agent systems into daily lives
crucially depends on the ability to develop effective policies for adjustable autonomy. Adjustable autonomy encompasses the strategies by which an agent selects the appropriate entity (itself, a human
user, or another agent) to make a decision at key moments when an action is required. We present two
formulations that address this issue: user-based and agent-based autonomy. Furthermore, we discuss
the current and future implications on systems composed of personal assistant agents, where autonomy
issues are of vital interest.