Ovarian reserve refers to the number of oocytes remaining in a woman's ovaries that have the potential to yield a pregnancy. This is a concept based on the fact that the number of oocytes within a woman's ovaries and her ability to achieve pregnancy decline over time. There are 2 overlapping but distinct interpretations and utilizations of ovarian reserve testing (ORT)-biological and clinical. Given the increasing incorporation of ORT into clinical practice, care must be taken to ensure that patients and providers understand the limitations affecting ORT interpretation. Here, we will review commonly used tests of ovarian reserve and offer guidance on interpretation (biology) and application (clinical practice) of results.