  The Galactic bulge is now considered to be the inner three-dimensional part
of the Milky Way's bar. It has a peanut shape and is characterized by
cylindrical rotation. In N-body simulations, box/peanut bulges arise from disks
through bar and buckling instabilities. Models of this kind explain much of the
structure and kinematics of the Galactic bulge and, in principle, also its
vertical metallicity gradient. Cosmological disk galaxy formation models with
high resolution and improved feedback models are now able to generate late-type
disk galaxies with disk-like or barred bulges. These bulges often contain an
early collapse stellar population and a population driven by later disk
instabilities. Due to the inside-out disk formation, these bulges can be
predominantly old, similar to the Milky Way bulge.
