  We describe the TreePM method for carrying out large N-Body simulations to
study formation and evolution of the large scale structure in the Universe.
This method is a combination of Barnes and Hut tree code and Particle-Mesh
code. It combines the automatic inclusion of periodic boundary conditions of PM
simulations with the high resolution of tree codes. This is done by splitting
the gravitational force into a short range and a long range component. We
describe the splitting of force between these two parts. We outline the key
differences between TreePM and some other N-Body methods.
