It is now well recognised that the magnetic fields on the Sun are the basic cause of this variability. Solar dynamo models that can predict the solar cycle are now possible (Choudhuri et al. 2007). Understanding how the magnetic fields are generated and maintained on the Sun, i.e. understanding the solar dynamo, hence, is basic to understanding the origin and nature of solar cycle and variability, and to predict in advance its behaviour both on short and long time scales.