Sizeism is a form of discrimination which is based on someone's size. This type of discrimination can take a number of forms, ranging from refusing to hire someone because he or she is too short, to treating overweight individuals with disdain. In some regions, laws are in place to prohibit sizeism, but sizeist attitudes are often deeply ingrained in society, which can make fighting sizeism very difficult.

Sizeism can be based on height, weight, and both. Humans are an incredibly diverse species, which means that individuals can have a wide range of sizes. Depending on where in the world one is, people may have a tendency to be especially tall, slender, short, or plump, and many societies have internalized attitudes about size which come out in the form of sizeism. As a general rule, sizeist attitudes imply that someone believes that his or her size is superior to that of other people.

Like other forms of discrimination, sizeism isn't always explicit. It involves the perpetuation of stereotypes and attitudes which support those stereotypes, such as the idea that all fat people are lazy, or that all tall people are good basketball players. Sizeist attitudes can also take the form of expressions of physical disgust when confronted with people of differing sizes. Often, people are not fully aware that they are behaving in a way which could be considered sizeist, and sizeist attitudes often slip past without mention, even among people who are otherwise aware of harmful prejudices.

Any time someone makes a judgment about someone else on the basis of his or her size, this is an example of sizeism. When a decision is made not to hire someone because of size, this is also sizeist. Sizeism can also manifest in the form of language; terms like “beanpole” for tall people and “fat pig” for people who are overweight are sizeist epithets. People who are overweight often suffer from sizeism, due to attitudes about fat which are held in many cultures, but they are not the only humans who experience sizeism.

Recognizing the signs of sizeism in yourself are often the first step to combating this prejudice. Analyzing the behavior of others and being unafraid to question people's attitudes is just as important. As in the case of other “-isms,” educating people about sizeism and explaining why you find it offensive is the only way to make a cultural shift which will lead to a change in attitudes.