Post-translational modification of thiols to form a nitrosothiol (S-nitrosylation) is gaining attention as a mechanism by which nitric oxide can exert some of its effects in the cardiovascular system, as well as in other systems. It has been proposed that this modification would have a particularly important role in cell signaling. However, its study has been hampered by many technical difficulties. In this paper, we summarize current achievements in the field that may help to answer the questions that have been posed about the functional role of this modification. Some of these achievements have arisen from methodologic improvements, such as proteomic studies or approaches to identify subcellular localization and tissue distribution of the modification. New functional consequences of the modification of individual proteins are also summarized.