The formation of the terrestrial planets is one of the fundamental origins problems. At the moment, we have only one observed example of terrestrial planets, the ones in our own Solar System. Therefore, theoretical modeling is the best means we have of understanding the formation process. I will present results from simulations of the buildup of planetesimals into planet size bodies, the influence of gas giant planets on terrestrial planet size and composition, and the implications these results have for finding terrestrial planets around other stars.