Adenomyosis is plagued by the presence of several different diagnostic definitions, all based on histology of the uterus. There have been a number of classification systems proposed, which will be discussed. The relationship between adenomyosis and natural fertility is a scientific vacuum, while in the field of IVF evidence is emerging that adenomyosis results in poorer outcomes both in live birth rates and pregnancy complications. Possible treatment options for this situation will be covered.