The massively parallel plasma simulation code P3D is a powerful tool for exploring the nonlinear dyanmics of 3-D plasma systems. It can be run as a full particle (particle electrons and ions), hybrid (particle ions and fluid, finite-mass electrons) or as a Hall MHD model. In the particle mode it solves the complete Maxwell equations and the equations of motion for the individual particles in two and three dimensions. The code has 3-D domain decomposition and communication between adjacent subdomains is implemented using MPI routines. The code routinely runs up to the limit of the available resources on parallel machines with 1 billion particles. The code has been operating in production mode for over a year on the 3-D reconnection problem.