What is the Kalam Cosmological Argument?

The Kalām cosmological argument is a modern formulation of the cosmological argument for the existence of God; named for the kalam (medieval Islamic scholasticism), it was popularized by William Lane Craig in hisThe Kalām Cosmological Argument (1979). 
Kalam cosmological argument as a brief syllogism, most commonly rendered as follows:

  1. Whatever begins to exist has a cause;
  2. The universe began to exist;
  3. Therefore, the universe has a cause.

…based upon ontological analysis of the properties of the cause:

  1. The universe has a cause;
  2. If the universe has a cause, then an uncaused, personal Creator of the universe exists who sans the universe is beginningless, changeless, immaterial, timeless, spaceless and enormously powerful;
  3. Therfore, An uncaused, personal Creator of the universe exists, who sans the universe is beginningless, changeless, immaterial, timeless, spaceless and infinitely powerful.

Source: Wikipedia