Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and
  Outstanding Issues
  This is the summary chapter of a review book on galaxy bulges. Bulge
properties and formation histories are more varied than those of ellipticals. I
emphasize two advances: 1 - "Classical bulges" are observationally
indistinguishable from ellipticals, and like them, are thought to form by major
galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming
(except in S0s) than are ellipticals. Theys are products of the slow
("secular") evolution of galaxy disks: bars and other nonaxisymmetries move
disk gas toward the center, where it starbursts and builds relatively flat,
rapidly rotating components. This secular evolution is a new area of galaxy
evolution work that complements hierarchical clustering. 2 - Disks of
high-redshift galaxies are unstable to the formation of mass clumps that sink
to the center and merge - an alternative channel for the formation of classical
bulges. I review successes and unsolved problems in the formation of
bulges+ellipticals and their coevolution (or not) with supermassive black
holes. I present an observer's perspective on simulations of dark matter galaxy
formation including baryons. I review how our picture of the quenching of star
formation is becoming general and secure at redshifts z < 1. The biggest
challenge is to produce realistic bulges+ellipticals and disks that overlap
over a factor of 10**3 in mass but that differ from each other as observed over
that whole range. Second, how does hierarchical clustering make so many giant,
bulgeless galaxies in field but not cluster environments? I argue that we rely
too much on AGN and star-formation feedback to solve these challenges.
