The uterus acts as a receptacle providing the home for the growing fetus from conception to the time of delivery. Globally most women deliver vaginally. The mechanism of onset of labour is still a speculation. Current theory is that hormonal change brought about by the hypothalamopituitary axis lowers progesterone, which is a muscle relaxant. This is followed by local changes in the chorioamnion that result in the production of prostaglandins, which cause softening and effacement of the cervix and uterine contractions that are key elements for the onset and progress of labour. Absent mechanical difficulties, uterine contractions bring about the process of cervical dilatation and descent of the head, resulting in spontaneous expulsion of the fetus, placenta and membranes. The main reasons for slow progress are inefficient uterine contractions (P-power), relative disproportion due to malposition, or cephalopelvic disproportion either due to a large baby and head (P-passenger) or a relatively small or non-gynaecoid pelvis (P-passage). These three Ps influence labour outcome.