This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. Philosophy of religion is a very varied and complex discipline, and there is a need to be very clear in your definitions and terminology. However, many religious believers would uphold the view that the sceptical philosopher is simply barking up the wrong tree by pinning down the theist and asking for definitions, as if that were all religious belief was about. It is a common misunderstanding that belief in God somehow rests upon the strength of the arguments for the existence of God. Undoubtedly, the arguments can strengthen a belief and it is very important to be able to support beliefs. However, belief in the existence of God does not rest upon philosophical speculation alone. When someone believes in the existence of God, he or she may well be defending a particular doctrinal viewpoint.