The purpose of this FOA is to encourage epidemiological, clinical and translational research that will increase our understanding of the presence of multiple chronic pain conditions in subjects with pain. Recent findings suggest substantial overlap may exist between chronic pain conditions. Individuals diagnosed with one disorder often exhibit characteristics of additional chronic painful conditions or transition to other diagnostic categories. A better understanding is needed of the prevalence of overlapping pain conditions, their underlying etiologies, the evolution of these overlaps, and the therapeutic approaches best suited for treating subjects with these conditions. The main objective of this FOA is the formation of research groups with research interests bridging expertise in pain mechanisms and translational and clinical expertise to address important unresolved questions about overlapping pain conditions.