Epidemiological studies have demonstrated that osteoarthritis (OA) is a complex trait with numerous environmental and genetic risk factors. A great deal of effort has been spent elucidating these risk factors and progress has been made. It is clear however that the causes behind OA development and progression continue to remain largely elusive. Identification of those genes that, in conjunction with environmental factors, predispose to OA severity will lead to a better understanding of the mechanisms underlying disease development and thus promote improved health strategies for prevention. An understanding of the molecular signalling pathways involved in the initiation and progression of the disease will improve clinical diagnosis and help identify improved, tailored treatment regimens. This chapter focuses on these issues, exploring the heritability of OA, known genetic risk factors, and specific traits and outcomes studied in the genetics of OA.