While red beans and kidney beans can be used interchangeably in most recipes and both have a deep red color, they are actually two different varieties of legumes.
Red beans are smaller than kidney beans but of similar shape. Used in many Southern and Creole dishes, they are sometimes called Mexican red beans. They can be found in a variety of foods, ranging from soups to salads to chili. The adzuki bean, which is often used in oriental dishes, is another variety of red bean. The adzuki bean is sweeter in taste and easier to digest.
Kidney beans get their name from their shape. Larger than red beans, they are part of many Southwestern dishes and are sometimes used as a meat substitute in Mexican tacos. These beans keep their shape when cooked and tend to absorb the flavors of accompanying foods.
Some recipes, like rice and beans, will offer a choice of either kidney beans or red beans in the ingredient list. Despite their subtle differences in size and taste, kidney beans are higher in protein and most minerals than red beans. An excellent source of fiber, kidney beans are slightly higher in calories.