There is no single “best” book — the best one is the one that answers the question you actually have, for the reader you actually are. That said, a few earn their reputation. For a modern beginner: Karl Keating’s Catholicism and Fundamentalism, Peter Kreeft and Ronald Tacelli’s Handbook of Christian Apologetics, and — for the human side of conversion — Scott and Kimberly Hahn’s Rome Sweet Home. All three are clear, charitable, and assume no special training.

Then graduate to the classics, which have outlived every fad. G.K. Chesterton’s Orthodoxy1 and The Everlasting Man argue by imagination and common sense; Frank Sheed’s Theology and Sanity trains you to think with the Faith; St. Francis de Sales’ The Catholic Controversy remains the model of charitable polemic; and John Henry Newman’s Essay on the Development of Christian Doctrine2 is the most important book ever written on how doctrine can grow without changing — the backbone of the continuity argument itself.

But the deepest apologetics library is the oldest one: Scripture, the Catechism, and the Church Fathers in their own words (Jurgens’ three-volume Faith of the Early Fathers is the standard gateway). Read the primary sources before the books about them — a secondary author can be wrong, and only the original lets you catch it. Match the book to the moment, remember that all of them exist to defend one concrete claim — that Christ founded a Church with authority to teach — and recall that even St. Paul, in prison, asked Timothy to “bring the books” (2 Timothy 4:13).