Adenomyosis is a benign uterine disorder in which endometrial glands and stroma are pathologically demonstrated in the uterine myometrium and it is considered a specific entity in the PALM-COEIN FIGO (polyp; adenomyosis; leiomyoma; malignancy and hyperplasia; coagulopathy; ovulatory dysfunction; endometrial; iatrogenic; and not yet classified - International Federation of Gynecology and Obstetrics) classification of causes of abnormal uterine bleeding (AUB). Although it has always been considered the classic condition of multiparous women over 40 years old who have pain and heavy menstrual bleeding, diagnosed at hysterectomy, the epidemiological scenario has completely changed. Adenomyosis is increasingly identified in young women with pain, AUB, infertility, or no symptoms by using imaging techniques such as transvaginal ultrasound and magnetic resonance. However, there is no agreement on the definition and classification of adenomyotic lesions from both the histopathology and the imaging point of view, and the diagnosis remains difficult and unclear. A uniform and shared reporting system needs to be implemented in order to improve our understanding on imaging features, their relationship with pathogenic theories, and their importance in terms of clinical symptoms and response to treatment. In fact, adenomyosis pathogenesis remains elusive and not a single theory can explain all of the different phenotypes of the disease. Furthermore, adenomyosis often coexists with other gynecological conditions, such as endometriosis and uterine fibroids, increasing the heterogeneity of available data. Treatment requires a lifelong management plan as the disease has a negative impact on quality of life in terms of menstrual symptoms, fertility, and pregnancy outcome and has a high risk of miscarriage and obstetric complications.