The purpose of this Funding Opportunity Announcement (FOA) is to encourage epidemiological, clinical and translational research that will increase our understanding of the natural history, prevalence, biological mechanisms, psychological variables, and clinical risk factors responsible for the presence of multiple chronic pain conditions in people with pain. Recent clinical findings suggest that 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, the underlying etiologies, the progression of these conditions, 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 interests bridging expertise in pain mechanisms with translational and clinical expertise to address important unresolved questions about overlapping pain conditions. Applicants are encouraged to leverage existing and develop new resources pertinent to the study of these conditions. Applicants are encouraged to include researchers with complementary expertise from outside the pain field in their research teams who will enhance the breadth of research and understanding of comorbid chronic pain conditions.