The kalam cosmological argument (KCA) for God’s existence goes as follows: 

(1) Everything that begins to exist has a cause
(2) The universe began to exist
(3) Therefore, the universe has a cause

When we consider what kind of cause would be necessary to bring the universe into being, we arrive at an immaterial, eternal, spaceless, personal, intelligent, and powerful being – an apt description of what theists identify as God.  Atheists commonly object and theists often wonder, “Well, then who made God?”  Theists rightly point out that the argument does not claim everything has a cause, but only those things that begin to exist.  As an eternal being, God never began to exist, and thus does not need a cause.  Indeed, the question itself is nonsensical given the kind of being God is. 

We apologists must be careful, however, not to think that the 1st premise of the KCA proves God does not have a cause.  The premise only pertains to things which begin to exist.  We cannot infer anything about the causal requirements or lack thereof for eternal beings from this premise.  While the 1st premise of the KCA does not require that God have a cause, to think it proves God does not have a cause is to commit the fallacy of denying the antecedent:

(1) If A, then B [If Bono is an American citizen, then he is a human being]
(2) Not A [Bono is not an American citizen]
(3) Therefore not B [Therefore Bono is not a human being]

Applied to the 1st premise of the KCA, the fallacy works this way:

(1) If A, then B [If X begins to exist, X has a cause]
(2) Not A [X did not begin to exist]
(3) Therefore not B [Therefore X does not have a cause]

The 1st premise of the KCA only tells you that contingent things require a cause, not that eternal things do not require a cause.  It could be the case that all things – including those that never begin to exist – need a cause.  Like the eternal indentation caused by an eternal ball resting on an eternal cushion from eternity past, it is at least possible that the cause of the universe requires a logically prior cause.

If we are going to conclude that God has no cause, a separate argument is needed. One way to argue that God cannot be caused is by demonstrating the incoherence of an infinite past.  To terminate an otherwise infinite regress, we need an uncaused causer (which is what theists understand God to be). This first cause, by virtue of being the first cause, cannot have a temporally/logically prior cause.  And given Ockham’s Razor, which says we should not multiply entities beyond necessity, there is no reason to think the cause of the universe has a logically prior cause apart from some argument to the contrary.[1]  

Another way of demonstrating that God has no cause is by offering a successful ontological argument.  If God is the greatest conceivable being, and it is greater to have being within oneself rather than to derive it from a transcendent source, then God must be an uncaused being.

[1]Of course, to avoid the infinite regress one must eventually come to a being that has no temporal or logical cause; i.e. a being whose existence is necessary. So even if we think the cause of the universe may itself have a cause, that being—or one of the beings who preceded it—must be an uncaused being.