Hatha Yoga is not a style of Yoga, it is the term which describes all styles of physical yoga which include postures (asana) and breathing exercises (pranayama).  Although the postures which feature in Hatha Yoga classes are all pretty similar, the way in which they are practiced differs depending on the style of yoga and the teacher’s background.  There are many styles of Hatha Yoga – some of the the most familiar are Ashtanga, Iyengar and Sivananda.  Very often a Hatha Yoga class will include elements of the different styles the teacher has studied or practiced.