The simulation of the motion of interacting particles is a deceivingly simple, yet powerful and natural method for exploring physical systems as diverse as planetary dark matter and proteins, unsteady separated flows, and plasmas. Particle simulations of continuum and molecular phenomena can be formulated by following the motion of interacting particles that carry the physical properties of the flow. In this talk we discuss particle methods with an emphasis on the utilization in flow simulations. We present multi resolution particle methods for vortical flows and hybrid molecular- continuum simulations for flows past carbon nanotubes. The extension of particle simulations to domains ranging from cell biology to virtual surgery will be discussed.