A number of organizations train and certify yoga teachers and several organizations set or recognize standards for yoga teacher training. The International Yoga Federation and the Yoga Alliance are two such groups.
When a practitioner is looking for a yoga teacher, they should examine that teacher's training and credentials as well as the style of yoga that will best suit their needs. The Yoga Alliance classifies these styles as gentle, spiritually-oriented, flow, alignment-oriented, fitness, hot or specialty yoga.
Yoga teachers who take a holistic approach are guides as well as instructors. They live their yoga practices and attempt to teach that way of life. These teachers apply the ethical and spiritual principles of yoga to their own lives and their instruction.
For example, the Yoga Sutras describe yoga as having eight limbs, so a classical yoga teacher would include these limbs as part of their instruction. In addition to teaching asanas and pranayama (breathing exercises), the instructor would also include yamas and niyamas (virtues and rules of living), pratyahara (control of the senses), dharana (inner awareness), dhyana (devotion) and samadhi (union with the Divine).
Teachers will typically identify with a particular tradition or lineage of yoga. Among these many traditions, there are: Ashtanga yoga, Hatha yoga, Inyengar yoga, Kundalini yoga, Tantra yoga, Yin yoga, Vinyasa yoga, Hot yoga, Power yoga or even a hybrid of disciplines.