2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/15093HI spectral line mapping studies are a unique probe of morphologically peculiar systems. Not only does HI imaging often reveal peculiarities that are totally unsuspected at optical wavelengths, but it opens a kinematic window into the outer dynamics of these systems that is unmatched at any other wavelength. In this review I attempt to summarize what we have learned from such studies, and what we may hope to learn from them in the future.10 pages, 5 figures, uses newpasp.sty, to appear in "Galaxy Dynamics: from the Early Universe to the Present", ASP Conf Series, eds F. Combes, G. Mamon and V. Charmandaris. Version with full-resolution figures available at http://www.cv.nrao.edu/~jhibbard/IAP15/iap15_review.ps.gzAstrophysicstext