We present the results of over 20 years of optical spectroscopic monitoring of the prototypical double-peaked emitter, Arp 102B. Its distinct double-peaked, extremely broad (FWHM ≈15,000 km s−1) low-ionization lines (Hα, Hβ, and Mg II) are well-modeled by emission from photoionized gas in a relativistic Keplerian accretion disk around a central black hole (Chen & Halpern 1989; Halpern et al. 1996). A ubiquitous property of double-peaked emitters is long-term variability in the shape of their line profiles on the timescale of months to years, which is consistent with the dynamical timescale of an accretion disk. This variability can be attributed to inhomogeneities in the line-emitting disk, i.e., hot spots, spiral arms, eccentricity, and warps. We characterize the profile variability of Arp 102B in detail, and use it to constrain physical models for the structure and dynamics of its line-emitting accretion disk.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html