In this paper, we discuss recent results on the propagation of dark spatial solitons (DSS). Dark spatial solitons are particular solutions of the nonlinear Schroedinger (NLS) equation modeling propagation of light beams in optical Kerr media. Experimental results are presented for three systems, including sodium vapor, various thermally nonlinear liquids, and the bulk semiconductor system ZnSe. The results of these investigations indicate that experimental dark spatial solitons obey the conservation laws of the NLS equation, possess collision properties characteristic of the theoretical DSS solutions, and are stable to external perturbations induced by the experiment. In addition, through an interferometric technique, we investigate the phase profile of the dark spatial solitons and show that it is in good agreement with the NLS solution. In addition to the fundamental DSS, we have performed experiments where nonfundamental DSS are excited in pairs by making use of an even initial field profile as originally discussed by Zakharov and Shabat. The transverse velocities of the solitons excited in the is manner are measured and found to be in good agreement with those predicted theoretically.