Endometriosis is a common gynecological condition, characterised by the presence of endometrial-like tissue outside the uterine cavity. It is estimated that endometriosis affects up to 10% of women during their reproductive years, causing debilitating pain and infertility. The aetiology of this condition remains poorly understood, however, evidence suggests that certain immune factors are almost certainly playing crucial roles in the pathogenesis and progression of this inflammatory condition. This book reviews research on endometriosis including endometriosis of the urinary tract; aromatase inhibitors as a new therapeutic option for endometriosis; endometriosis and its implications for fertility; laboratory and imaging diagnoses of endometriosis; various treatment options for endometriosis and others.