The process of fertilization is crucial for species development and maintenance. Due to social and environmental problems, the number of infertile couples is increasing worldwide. Male and female factors contribute equally, and about 7% of men experiences problems in conceiving a child due to sperm defects. Assisted reproduction techniques (ARTs), including the most invasive intracytoplasmic sperm injection (ICSI), are the only available therapy for severe male factor infertility. Whether such techniques are associated with increased birth defects is still debated, and search for alternative options should go on. A better understanding of the molecular mechanisms involved in the process of fertilization may lead to the development of new pharmacological strategies to treat infertile men and new male contraceptive agents. In addition, in view of the low predictive power of routine semen analysis, new tests aimed to better predict the fertilization potential could be developed. The present review summarizes current evidence of the molecular mechanisms involved in fertilization in human spermatozoa, with particular emphasis on the main post-ejaculatory maturation events, i.e. sperm capacitation and motility.