Which C.S. Lewis book presents the Christian idea of the four loves?

The C.S. Lewis book presenting the Christian idea of four kinds of love is The Four Loves.

Published in 1960, the book developed from a BBC radio talk broadcast in 1958. Lewis examines four Greek terms commonly used to distinguish forms of love: affection, friendship, erotic love, and charitable or self-giving love. In English editions, these are usually associated with storge, philia, eros, and agape.

Lewis does not treat the categories as isolated boxes. He explores how natural loves can be valuable while also becoming possessive or distorted when treated as ultimate. He presents agape, or divine love, as the form that gives and transforms the others.

The book is sometimes confused with Mere Christianity because both discuss Christian belief for a broad audience. Mere Christianity grew from wartime broadcasts and explains core Christian doctrines, whereas The Four Loves focuses on human relationships and divine love.