This chapter deals with the deeper zonal anatomy of the uterus and particularly with the role these areas have in controlling uterine movements. The morphology of the junctional zone (JZ) suggests a distinct compartment of myometrium, tightly packed with muscle cells with an increased vascularity, designed as it were for a specific purpose. The JZ is responsive to changes in sex steroid levels, and undergoes a cycle of change which parallels the changes in endometrial thickness. Rapidly developing technology allows better images and the introduction of ever more complex classification of JZ contractions (JZC). The frequent use of ultrasound during assisted conception cycles provides most of the information we have about JZC, with most data coming from the study of long protocol stimulation in vitro fertilization (IVF) cycles. Excessive JZC have been shown to reduce implantation rates in both spontaneous and stimulated cycles.