Bull fertility, defined as the ability of the spermatozoon to fertilize and activate the ovum and then support embryonic and even fetal development, is a crucial factor influencing animal reproduction and production efficiency. Despite significant influences of fertility on herd genetic improvement and efficient cattle production, the mechanisms regulating this phenotype and reliable biomarkers associated with bull fertility are poorly defined. Specifically, there is a broad lack of knowledge in bull fertility. In this paper, bull fertility is reviewed within the context of animal systems physiology, and system biology markers associated with bull fertility are provided. This mini-review is intended to be a useful resource for students, animal producers, and the general public to help understand and appreciate this economically important trait.