  We discuss the formation and evolution of boxy/peanut bulges (B/Ps) and
present new simulations results. Orbital structure studies show that B/Ps are
parts of bars seen edge-on, they have their origin in vertical instabilities of
the disc material and they are somewhat shorter in extent than bars. When the
bar forms it is vertically thin, but after a time of the order of a Gyr it
experiences a vertical instability and buckles. At that time the strength of
the bar decreases, its inner part becomes thicker, so that, seen edge-on, it
acquires a peanut or boxy shape. A second buckling episode is seen in
simulations with strong bars, accompanied by a further thickening of the B/P
and a weakening of the bar. Quantitatively, this evolution depends considerably
on the properties of the halo and particularly on the extent of its core. This
influences the amount of angular momentum exchanged within the galaxy, emitted
by near-resonant material in the bar region and absorbed by near-resonant
material in the halo and in the outer disc. Haloes with small cores generally
harbour stronger bars and B/Ps and they often witness double buckling.
