God only knows what I'd be without you, sang the Beach Boys in 1966. A certain item of knowledge is here attributed to God - knowledge, so it is said, that no-one else possesses. Some say that this knowledge behaves like that of a super-psychologist, while others say that it is middle knowledge - God knows what would have become of the singer in a non-actual world, given certain free decisions of others. This book collects all major contributions to the question whether middle knowledge is possible at all, and if so, what help it would be in spelling out, for example, the doctrine of divine providence.