The fertility of high yielding dairy cows has been declining over the past 25 years. Several studies have clearly demonstrated that the resumption of ovarian activity has been retarded and that conception rates have dropped significantly from 55 to 40%. Accordingly, the calving interval has increased from about 385 days to 412 days. The percentage of cows culled because of infertility has risen from 5 to 8% per year. This decrease in fertility results has led to a decline in the profitability of dairy herds. In a 100 cow herd this yearly loss amounts to at least 5000 euros. The ‘subfertility syndrome’ is a multifactorial problem in which, first and foremost, the period of negative energy balance and nutrition affect endocrine signaling, follicular growth and probably also oocyte and embryo quality. Although a lot of research has already been done, many problems still need to be unraveled. Solutions for this complex problem are difficult to achieve because they involve optimizing a whole series of critical factors such as housing and management, estrus detection, nutrition during the dry, transition and lactation periods, timing of insemination, hygiene and care around parturition, claw health and the use of good quality semen.