This chapter provides a critical review of key developments in understanding and improving boar reproductive efficiency, tracing its development from seminal discoveries to contemporary advances in artificial insemination (AI) and sperm analysis technologies. Key developments in identifying fertile boars are discussed, including sperm kinematics, proteomics, lipidomics, and flow cytometry, along with computer-assisted sperm analysis (CASA). Environmental influences, such as heat stress, sperm handling, and neonatal development, on semen quality and fertility are explored. Continued research in sperm cryopreservation, infertility diagnostics, and bacterial management to meet the growing global demand for pork will be necessary for continued improvement of boar fertility.