Realistic N-body simulations of open clusters are discussed and compared with main observed cluster features. Most of the models have 1000 bodies with initial masses following a power law mass function of slope α = -2.75. Instantaneous mass loss from stellar evolution; a smooth linearized galactic tidal field and transient shocks by encounters with extended interstellar clouds of different mass-spectrum, density and space concentration are included. Close approaches between particles are treated by a two-body regularization technique that allows to follow binary evolution in detail. Good agreement is found between the distribution of lifetime for galactic clusters and the life of the models. It is found that the combined action of evolutionary mass loss and binaries (for 1000 star clusters with a realistic mass function) is enough to arrest the core collapse. Tidal heating shapes the halo of the cluster and produces a distinctive density and velocity distribution. Encounters with standard clouds do not alter the life-time of the clusters; while giant molecular clouds produce a catastrophic disruption. Mass segregation and preferential escape of light stars can account for the depletion of low luminosity stars in the better observed central region of clusters. Work on the primordial stages of evolution of clusters during star formation is reviewed, and linked to work on
N-body clusters.