Oscillations of human insulin secretion have been studied for about 30 years. Two distinct types of oscillations will be discussed: ultradian oscillations with a period of 80-150 min, and more rapid 5-15 min secretory pulses. An ODE model of the ultradian oscillations will be presented. It will be demonstrated how the model accounts for many, but not all experimental results. Furthermore, experiments of the rapid pulses in the isolated perfused rat pancreas and in vivo in humans will be presented. A hypothesis for how the rapid pulses are modulated by glucose in vivo will be discussed.