  I present N-body simulations of isolated and interacting galaxies, made on
GRAPE machines. In particular I discuss the formation and evolution of N-body
bars and compare their properties to those of bars in early-type and late-type
galactic discs. I argue that the halo can help the bar grow, contrary to
previous beliefs, by taking positive angular momentum from it via its resonant
stars. I then focus on the interaction and subsequent merging of a barred disc
galaxy with a spheroidal satellite. The evolution depends strongly on the mass
(density) of the satellite and may lead to its destruction or to the
destruction of the bar.
