George Pólya (1887–1985) was a professor of mathematics at Stanford University who made lasting contributions to combinatorics, number theory, numerical analysis, and probability theory. He was also very well-known for his work in mathematics education. In his later days, Dr. Pólya spent considerable effort to document the methods that people use to solve problems, and to describe how problem-solving should be taught and learned. He wrote four books on the subject.