At present the orbit of asteroid (99942) Apophis and the forces acting on it are not known with sufficient accuracy to predict with certainty its motion after the close approach to the Earth in April of 2029. As a result of this approach the current heliocentric orbit of the asteroid will be changed by Earth's gravity. The amount of change depends substantially on the minimum geocentric distance of the asteroid during its close approach. We compare published solutions for Apophis' orbit and discuss the consequences that follow from the uncertainty of Apophis' orbit, including the probability of its collision with the Earth in April 2036. New determinations of Apophis' orbit that appeared after the end of the Conference ACH-2009 support our conclusion that the widely quoted value of Apophis' collision probability with the Earth in 2036 of 1/45000 is an overestimate.