Galaxy building

This review discusses the various processes that contribute to the building of galaxies, with emphasis on the direct observational evidence for these processes. The disks, bulges, and nuclei of galaxies are all probably built up over a significantly extended period of time by the continuing addition of matter, often in discrete amounts associated with the merging of smaller units. The information about galaxy formation available from the fossil record and from look-back observations is also reviewed, and it is concluded that the epochs of disk and spheroid formation can be identified and studied directly by observations at high redshifts, except perhaps for the earliest stage of spheroid formation which probably occurs at redshifts not yet observed. 193 refs