This chapter reviews the available literature on the clinical assessment of the endometrium. It focuses on the tools available to diagnose and treat both infertility and pregnancy loss. Infertility and recurrent pregnancy loss are often attributable to implantation failure. The mechanism of implantation varies widely between species, reflecting the evolving conflicts between maternal and embryonic interests. Serum progesterone measurements are a mainstay of hormonal assessment to document ovulation and appear to correlate well with endometrial biopsy results. Doppler flow studies are non-invasive ultrasound methods used to evaluate the blood flow to the uterus and endometrium. Causes of repeat in-vitro fertilization (IVF) failure that are related to endometrial receptivity defects have recently been reviewed. Cost and side effects of treatments will be reduced as clinical assessment of the endometrium yields more information about the causes of infertility or pregnancy loss.