Hatha Yoga (means to produce balance and power) is one of two branches of yoga (the other is Raja Yoga) that focuses on the physical culture. Both these types of yoga are referred to as Sadanga Yoga.
Hatha Yoga comprises both postures and breathing exercises. Postures are called "Asanas" whereas breathing is called "Pranayama". Pranayama can be practised by beginners quite safely although more advanced forms of Pranayama should be undertaken with the guidance of a yoga teacher.
Yoga is currently booming in the western world, with over 16 million people practising it in the US in 2005.