  I discuss several aspects of secular evolution linked to bars and to
boxy/peanut bulges, based on a very large number of high resolution, fully
self-consistent $N$-body simulations. When the bar forms, it is as thin as the
disc. Its three-dimensional shape, however, evolves, so that, at later times,
it has a thick inner part and a thin, more extended outer part. The former,
when viewed edge-on, is called a boxy/peanut bulge, because of its shape. The
strength of the box/peanut correlates with the bar strength, the strongest
cases having formed after two buckling episodes. The extent of the box/peanut
is considerably shorter than the bar length, in good agreement with orbital
structure studies and with observations. Viewed at an angle near to, but not
quite edge-on, barred galaxies show specific isodensity/isophotal shapes, which
are different in the thick and in the thin part of the bar. The isophotes of
M31 also have such shapes. This, taken together with radial photometric
profiles and kinematics, argue that M31 is a barred galaxy. Thus, the
pseudo-ring seen at roughly 50' could be an outer ring formed at the outer
Lindblad resonance of the bar.
