In general terms, the use of endometrial cytology is less common amongst veterinary practitioners compared to the use of endometrial culture, particularly in busy private practices. This chapter focuses on the most common techniques for collecting and processing samples for cytological analysis and their interpretation. The acquisition of cytological samples is most commonly done during midestrus, since at this stage of the cycle the cervix is open and the uterine immune mechanisms are more active. Hence, the likelihood of finding inflammatory cells (neutrophils) or bacteria will be increased. Recent studies have suggested that the use of uterine lavage is advantageous in correctly diagnosing mares that suffer from endometritis, compared to the use of swabbing techniques alone. The main goal of endometrial cytology is to determine the presence of cellular associations indicative of an active inflammatory response in the uterus.