Both figuratively and literally, bulges are central to our understanding of most disk galaxies. The so-called “super-thins” apart, bulgeless disks with extreme axial ratios (Karachentsev, Karachentseva, & Parnovskij 1993), most disks possess a central spheroidal-like component called the bulge (better defined as the central excess over the inward extrapolation of the outer exponential disk; Carollo, Ferguson, & Wyse 1999). In fact, the bulge-to-disk ratio is a defining property of the Hubble classification for spirals. In many cases, the bulge dominates the central potential, it determines the position of major resonances, and bulges are now known to be intimately linked to massive central black holes (BHs; Magorrian et al. 1998). Bulges thus play an active role in the structure, dynamics, and evolution of the galaxies in which they are embedded.
Writing an exhaustive review in the space allocated is impossible, so only selected topics related to the structure, kinematics, and dynamics of bulges will be discussed. Issues regarding stellar populations will mostly be left out, and clues to bulge evolution shall be noted only when directly relevant to the issue at hand. The common thread will be to emphasize similarities and differences between ellipticals and bulges on the one hand, and bulges and disks on the other. Topics to be discussed include a brief historical review (§ 2), the fundamental plane (FP) of bulges (§ 3), their light distribution (§ 4), 3D structure (§ 5), nuclear properties (§ 6), and large-scale mass distribution (§ 7). The conclusions (§ 8) will illustrate the perspectives offered by panoramic integral-field spectrographs and new or recent instruments.