Bovine cervical mucus changes its biochemical composition and biophysical properties due to the variations in sex steroid levels during the oestrous cycle. As a consequence of oestro- gen rise, cervical mucus is produced in larger amounts at oestrus—a stage also characterized by an increase in mucus crystallization when observed under light microscopy. The objective of this article is to provide an updated review of the main aspects regarding crystallization of bovine cervical mucus. First, it makes reference to the composition of cervical mucus and the critical functions that this secretion exerts on bovine reproductive physiology, as well as in other species. Then, the article deals with the phenomenon of crystallization observed in cervical mucus, describing the main models used to classify the crystalline patterns ob- servable in mucus at oestrus stage (some of them resembling ferns, palm leaves and stellar patterns, among others). Finally, it addresses the importance of the phenomenon of cervical mucus crystallization for the understanding of bovine reproductive physiology.