What Is Sivananda Yoga?

Swami Sivananda was a great sage in the early 1900s in India. He had many disciples. One such disciple of Swami Sivananda was Swami Vishnudevananda. Swamiji, as he is known as, had a short career in the army before he came to accidentally know of the teachings of Swami Sivananda via one of his books. This took him to meet his Master in Rishikesh. 
Swamiji entered the Sivananda Ashram in Rishikesh in 1947 at the age of 20 and became a monk. He trained thousands of students in the Ashram, both Indian and Western. He lived and worked under the guidance of Swami Sivananda for 10 years before Swami Sivananda sent him to the West to spread the word of yoga. 
Swami Vishnudevananda travelled throughout North America, teaching yoga and observing the Western lifestyle.
After his observations, he condensed the historic teachings of yoga into 5 points. These 5 points are:
1 - Proper Exercise
2 - Proper Breathing
3 - Proper Relaxation
4 - Proper Diet
5 - Positive Thinking and Meditation

Proper exercise involves gentle movement in the body to stretch the muscles and keep the spine strong and healthy. It is the practice of the asanas (postures). Your body is the temple where your soul resides therefore it needs to be kept healthy and clean.
Proper breathing involves abdominal breathing to energise the body and use the lungs' full capacity. Pranayama breathing practices help to calm the mind.
Proper relaxation involves allowing the physical body to rest and relax, the mind to become still and the soul to reconnect with its true nature - that of bliss and happiness.
Proper diet involves healthy eating habits, organic and fresh foods and a balanced diet, preferably vegetarian. 
Positive thinking and meditation involves counteracting negative thoughts with positive ones. Meditation involves focusing and concentrating the mind on one thing, bringing the mind under control and observing the actions of the mind.
Swamiji condensed the teachings of yoga into these 5 points so Western cultures could incorporate yoga into their every day lives.