Combinatory logic is a versatile field that is connected to philosophical, mathematical, and computational logic. This comprehensive reference on combinatory logic covers results in the field from the last four decades along with classical information on the topic. The author makes combinatory logic simple to understand while providing working knowledge that is rigorous, current, and readable. Reader-friendly without compromising the precision of exposition, the book includes many new research results not found in the available literature. It also contains pointers to new directions in the field that can be pursued further by researchers.