Physiology of the first stage of labor is described in detail with the help of 6 well illustrated diagrams. Labor, onset and stages of labor, impending labor, physiological changes in the uterus during labor, procedure of vaginal examination are described comprehensively. Stages of labor, false labor, premature rupture of membranes, causes of onset of labor, contraction and retraction, ripening of cervix and level and station of presenting parts during labor are given in detail separately. 1 table is included to facilitate learning. 6 learning objectives are given in the beginning of chapter for better understanding of the subject. 6 references are given at the end of chapter for further reading.