Psychology is the science of behavior and mental processes. Many psychologists work with people to understand how they think, respond to stress, learn and forget, develop into unique personalities, and interact with one another. Others study the behavior and nervous systems of animals in order to find general principles that apply across species. Psychologists apply their knowledge to do therapy and counseling, to improve practices in schools, prisons, and rehabilitation centers, and to enhance performance in industry, business, and the professions. Careers in psychology are already plentiful and fulfilling, and the field is one of the fastest growing in the world.