History knows many examples of true friendship. The Old Testament tells about the amazingly deep relationship between David and Jonathan. Saints Basil the Great and Gregory the Theologian carried their friendship from their youth until the end of their lives. The Savior Himself calls His disciples friends. Friendship in its highest manifestation is a feat, service and an image of the Kingdom of Heaven. The statements of the holy fathers and religious thinkers collected in this book are intended to instruct us in the science of friendship, so that, by learning friendly love, we become true friends of Christ.