The link between varicoceles and male infertility has been a matter of debate for more than half a century. Varicocele is considered the most common correctable cause of male infertility, but some men with varicoceles are able to father children, even without intervention. In addition, improvements in semen quality after varicocelectomy do not always result in spontaneous pregnancy. Studies regarding possible pathophysiological mechanisms behind varicocele-induced infertility have tried to address these controversies. Oxidative stress seems to be a central mechanism; however, no single theory is able to explain the differential effect of varicoceles on infertility. As a consequence, careful patient selection for treatment based on couple fertility status, varicocele grade, and semen quality is critical for achieving a chance of a subsequent pregnancy. A substantial amount of data on the effects of varicocelectomy has been gathered, but inadequate study design and considerable heterogeneity of available studies mean that these data are rarely conclusive. Current evidence suggests a beneficial effect of varicocelectomy on semen quality and pregnancy outcomes in couples with documented infertility only if the male partner has a clinically palpable varicocele and affected semen parameters.