The recognition of hydrogen sulfide (H(2)S) as an endogenously produced gas with signaling potential has stimulated research on a multitude of physiological effects mediated in the cardiovascular, immune, gastrointestinal, genitourinary, endocrine, and central nervous systems. The heightened activity in the area of H(2)S biology led to convening of the first international conference on H(2)S in Shanghai in the summer of 2009 and to two Forum issues published in 2010 by Antioxidants & Redox Signaling on the physiological effects of H(2)S. Yet, fundamental questions regarding the biogenesis and regulation of H(2)S, the bioenergetics of its catabolism, its tissue concentrations, and elucidation of its molecular targets remain. Some of these issues are the subject of the current Forum on H(2)S.