Health at Every Size (HAES) is a philosophy which takes the immense variation of the human form into account, stating that it is possible for people of a range of sizes and shapes to be healthy. Many people associate the HAES concept specifically with the fat acceptance movement, but it is in fact open to people of all sizes, and people from a wide range of communities support the idea. This philosophy is designed to approach health from a weight-neutral approach, encouraging people to be happy, fit, and healthy no matter how large they are.

The root concept behind Health at Every Size is not that everyone is automatically healthy, no matter how large they are. Proponents of Health at Every Size merely believe that it is possible for people of all sizes to be healthy, if they want to invest time and energy in developing a healthy diet and exercise plan. Rather than considering size as a diagnostic criterion for health, people who believe in Health at Any Size think that size is not in fact relevant to someone's health.

Most supporters of Health at Every Size agree that there are two fundamental approaches to getting and remaining healthy: diet and exercise. “Diet” under the HAES paradigm does not refer to excessive calorie restriction to reach a desired goal weight, but rather to the consumption of a diet which is balanced, nutritious, healthy, and enjoyable. Since human bodies are dramatically different, the details of a healthy diet may vary from person to person, and members of the Health at Every Size movement encourage people to work with nutritionists to develop the ideal diet, creating a system of intuitive eating which is satisfying and good for you.

Exercise is also an extremely important component to good health, as numerous studies conducted around the world have shown. Supporters of the concept of Health at Any Size argue that it is possible to be skinny and unhealthy if one does not exercise, and to be fat and healthy if one exercises. Exercise can also take a wide variety of forms, including things like walking, cycling, swimming, and even belly dancing along with mountain climbing, competitive sports, and a range of other activities which are designed to keep bodies fit, healthy, and happy by getting them moving.

HAES is not meant to promote being fat, skinny, or any size in-between, but rather it encourages people to find weights at which they are healthy and happy. Proponents hope that by advancing the idea that it is possible to be healthy in a wide range of sizes, people at extremes of the size scale may face less discrimination and social commentary.