Due to the co-locations and options to co-register, the registration is a bit more complicated than usual. All relevant information is given on the registration page.
Note: authors of accepted Workshop Papers, Demos, or Doctoral Consortium submissions may register until the late registration deadline, April 9, for the price of an early registration (deadline March 12). To do so, follow the above link to the AAAI registration page, and follow this procedure:
445 Burgess Drive
Menlo Park, CA 94025