Kormendy (1982a, b) suggested that what we now call pseudobulges were built by secular inward gas transport and star formation. Combes & Sanders (1981) suggested that boxy bulges formed from bars that heat themselves in the axial direction. Pfenniger & Norman (1990) discuss both processes. These themes - dissipational and dissipationless, secular pseudobulge building - have persisted in the literature ever since (see Kormendy & Kennicutt 2004).
How can we tell whether a "bulge" formed by these processes? Fortunately, pseudobulges retain enough memory of their disky origin so that the best examples are recognizable. Structural features that indicate a disky origin include nuclear bars, nuclear disks, nuclear spiral structure, boxy bulges, exponential bulges, and central star formation (Figures 3 and 4). We consider all of these to be features of pseudobulges, because the evidence is that all of them are built secularly out of disk material. Similarly, global spiral structure, flocculent spiral structure, and no spiral structure in S0 galaxies are all features of disks. In addition, pseudobulges are more dominated by rotation and less dominated by random motions than are classical bulges and ellipticals.
Spectacular progress in recent years has come from HST imaging surveys. We begin with these surveys. To make data available on more galaxies, we also provide a detailed discussion of two galaxies, NGC 4371 and NGC 3945, that are different from the ones discussed in Kormendy & Kennicutt (2004).