Aristotle (384-322bc) was one of the leading intellectual figures of all time. In his work he systematised a massive amount of knowledge on a diverse range of subjects, including medicine. This article discusses the observations and hypotheses of this great philosopher on semen and infertility, as they are presented in his work Generation of Animals. This is combined with an evaluation of his positions in relation to those of the Hippocratic Corpus on the same subject. An extensive review of Aristotle's work Generation of Animals was performed with particular focus on his perspectives about semen and infertility. Publications referring to this work were also reviewed. According to Aristotle, semen is that which contains the principles that come from both parents when they unite. He believed that semen was formed by the secretion of nutriments by the body, developing his theories of sterility on this basic principle. A lack of fertility is attributed to genetic or acquired causes. He proposed methods for diagnosing sterility, primarily the 'water test' for men and the 'pessary' method for women. Even if his observations contain clear mistakes, such as attributing only secondary functions to male testicles and the identification of menses as women's 'seed', Aristotle's views also contain keen observations and exceptional thinking, both on the characteristics of semen and the causes of sterility (infertility).