The concept of ovarian reserve describes the natural oocyte endowment and is closely associated with female age, which is the single most important factor influencing reproductive outcome. Fertility potential first declines after the age of 30 and moves downward rapidly thereafter, essentially reaching zero by the mid-40s. Conceptions beyond this age are exceedingly rare, unless oocytes obtained from a younger donor are utilised. How best to estimate ovarian reserve clinically remains controversial. Passive assessments of ovarian reserve include measurement of serum follicle stimulating hormone (FSH), oestradiol (E(2)), anti-Müllerian hormone (AMH), and inhibin-B. Ultrasound determination of antral follicle count (AFC), ovarian vascularity and ovarian volume also can have a role. The clomiphene citrate challenge test (CCCT), exogenous FSH ovarian reserve test (EFORT), and GnRH-agonist stimulation test (GAST) are provocative methods that have been used to assess ovarian reserve. Importantly, a patient's prior response to gonadotropins also provides highly valuable information about ovarian function. Regarding prediction of reproductive outcome, in vitro fertilisation (IVF) experience at our centres and elsewhere has shown that some assessments of ovarian reserve perform better than others. In this report, these tests are discussed and compared; we also present practical strategies to organise screening as presently used at our institutions. Experimental challenges to the long-held tenet of irreversible ovarian ageing are also introduced and explored. While pregnancy rates after IVF are influenced by multiple (non-ovarian) factors including in vitro laboratory conditions, semen parameters, psychological stress and technique of embryo transfer, predicting response to gonadotropin treatment nevertheless remains an important aim in the evaluation of the couple struggling with infertility.