Evidence of infertility complications dates back to biblical times, when the foremother, Sarah, failed to conceive. Many centuries later, in 1667 the Danish scientist Anton van Leeuwenhoek, a glazier by profession, serendipitously invented a magnifying glass and in 1674 Nicolaas Hartsoeker, a Dutch scientist, assisted by Leeuwenhoek, found sperm cells in the seminal fluid under magnification (Figure 0.1). Observing human sperm through a microscope, Hartsoeker believed that he saw tiny men inside the sperm, which he called Homunculus. The theory of Homunculus (1694) claimed that a tiny, formed child exists in the head of the sperm cell, which becomes engulfed in the uterus, where it grows as if in an incubator until the moment of birth (Figure 0.2). It was then that the idea of in vitro fertilization (IVF) was born, i.e., to grow a child in a laboratory flask instead of in the mother’s womb. The understanding that the embryo is formed by fertilization of the oocyte by the sperm cell came only later.