Adenomyosis is a benign gynecological disease frequently affecting women of reproductive age. It has a negative impact on the quality of life, causing bleeding disorders, dysmenorrhea, chronic pelvic pain, and infertility. However, the molecular mechanisms involved in adenomyosis development remain unclear. This paper summarizes the reports found in the MEDLINE database on the molecular mechanisms involved in the development and progression of uterine adenomyosis. The literature search included the following terms: “adenomyosis,” “adenomyoma,” “pathogenesis,” “molecular mechanisms,” and “gynecological disorders.” Only peer-reviewed, English-language journal articles were included. This review focuses on the molecular genetics, epigenetic modifications, and pivotal signaling pathways associated with adenomyosis development and progression, which will provide insights into and a better understanding of its underlying pathophysiology.