This chapter basically talks about the endometrium: benign lesions. Endometrium is divided into superficial stratum functionalis and deeper stratum basalis. Stratum Functionalis is the superficial thick functional layer that is sloughed out at the time of menstruation. The stratum functionalis part is richly vascularized by the spiral arteries. Stratum Basalis is the basal portion of the endometrium. The regeneration of the superficial endometrium after menstruation occurs from the stratum basalis. The endometrium undergoes cyclical changes consisting of proliferative phase, secretory phase and menstrual phase. This chapter also discusses the endometrial dating and biopsy, postmenopausal endometrium, pregnancy-induced changes, artifacts in endometrium and dysfunctional uterine bleeding. This chapter also describes the hormone-induced changes, endometritis, endometrial polyp, adenomyomatous polyp and atypical polypoid adenomyoma. Endometrial metaplastic and reactive changes, Asherman’s syndrome and endometriosis are also discussed in this chapter.