Molecular modeling is a collective term that refers to theoretical methods and computational techniques to model and mimic the behavior of molecules, such as visualizing two- and three-dimensional (2D and 3D) structures, organizing compounds and their properties into databases, providing tools for analyzing molecular properties, or simulating the behavior of molecules on an atomic level. Drug design is an iterative process that begins when a compound is identified to display an interesting biological profile and ends when its activity profile and the chemical synthesis are optimized. Today, molecular modeling permeates all aspects of drug design. Scientists have used computer models of new chemical entities to help define activity profiles, geometries, and reactivities.