Ayurveda is the world's oldest and most comprehensive natural system of health care.
Ayus = Lifespan or Longevity
Veda = Knowledge
Thus Ayurveda translates as "knowledge of long life".
The easiest way to understand the approach of Ayurveda is to review the description of nature that modern physics gives us. Physics tells us the world exists in layers. The surface levels of nature behave like particles and are the domain of classical physics. The deeper, more subtle levels of nature behave like wave patterns in a field (Unified Field) and are the domain of quantum physics. Ayurveda is a health care system based on an analysis of health from the deepest quantum mechanical level in nature.
Ayurveda evaluates all issues in health from the perspective of the Unified Field and its first manifestations. The approach comes from the direct cognition, or experience, of the Vedic Rishis. Rishi means seer. Vedic Rishis purified and refined the functioning of their nervous systems until they could consciously experience and perceive the Unified Field and it's functioning from deep within their own minds. Their cognitions of the laws of nature functioning on this deepest quantum mechanical level became the body of knowledge called the Veda.
The Vedic Rishis described three fundamental fields that are the first expressions of the Unified Field. These fields orchestrate the functioning of the entire physiology on grosser, more manifest levels. Ayurveda calls these three fields (or doshas); Vata, Pitta and Kapha and gives detailed descriptions of their structure and activity within the body.
According to Ayurveda, all disease is caused by imbalances that are present in Vata, Pitta and Kapha. Imbalance in the doshas is imbalance in the body's inner intelligence responsible for proper functioning of all the grosser, more material aspects of the physiology. Treating Vata, Pitta and Kapha is equivalent to enlivening the body's natural healing, balancing and self-repair processes.
There are many ways Ayurveda prescribes for balancing the doshas; these include diet, herbs and lifestyle routines.
I highly recommed Deepak Chopra's book, "Perfect Health" as a fabulous reference book on Ayurveda.