The general definition of infertility is a lesser capacity to conceive than the mean capacity of the general population and infertile couples can be characterized in two groups: those unable to conceive without therapy and those who are hypofertile, but conceive without therapy. The initial diagnostic tests for infertility should include a midluteal phase progesterone assay, a semen analysis and a test for tubal patency such as a hysterosalpingogram. Measuring progesterone is the best test for confirming ovulation. To predict ovulation, evaluating the luteinizing hormone (LH) surge is the best single assay while measurement of LH plus preovulatory oestrogen is the best prediction. Today primary investigation of the morphology of the uterus and tubes should be by hysterosalpingography. However, ultrasound, particularly with simple contrast media, is likely to gain in importance. Laparoscopy should be reserved as a further diagnostic procedure or in combination with endoscopic surgery. There are situations in which semen analysis is of utmost importance and of absolute predictive value, namely, in cases of azoospermia. In general semen analysis remains a substantial part of the fertility workup, but any consideration of its predictive value has to be cautious. Performing genetic tests before, during and after assisted reproductive techniques (ART) is an intrinsic part of good clinical practice. These tests allow one to reach a correct diagnosis, to give adequate genetic counselling to the couple and their families in cases such as (i) women with Turner syndrome; (ii) men with 47, XXY; (iii) men or women with structural chromosomal aberration; (iv) men with Yq11 deletion or (v) men with congenital bilateral absence of vas deferens. Patients should, of course, be made aware of the occurrence of de-novo mutations taking place in the testis and in the embryo. Treatment of some causes of infertility are of proven value. For example induction of ovulation. Others are more controversial. Among the many empirical treatments suggested for the treatment of the various form of subfertility, surgical treatment of varicocele in the male, treatment of pelvic endometriosis in the female and the efficacy of the ART strategies offered to the subfertile couple are considered. Many varicocele studies are of poor quality. A few are good, but small in size. They do not show an improvement in pregnancy rates. Therefore, at the moment, there is insufficient scientific evidence for recommending routinely surgical treatment in subfertile and/or oligozoospermic men with a varicocele. Randomized, double-blind controlled trials demonstrated the modest efficacy of endometriosis ablation in increasing the pregnancy rate in infertile women while drugs suppressing ovulation are of no benefit to infertile women with endometriosis. Although the largest body of evidence available suggests that IVF success declines in repeated ART cycles, an accurate estimate of the true success rate in the 'nth' cycle of IVF treatment is not possible. Similarly little is still known of the reasons for the overall low continuation rates with IVF treatment.