The article presents a discussion on molecular dynamics (MD) simulation. MD requires a description of the molecules and the forces that act between them; a well known example is the Lennard-Jones potential, in which spherical particles repel one another at close range but otherwise attract. The MD simulation itself amounts to numerically integrating the equations of motion for systems of between a few hundred and a few million particles over many thousand (or more) timesteps. The paths the particles follow during the computation represent actual molecular trajectories. What does the future hold? MD simulation covers length scales ranging from the atomistic to entire microstructures. It has proved capable of studying a broad range of phenomena associated with both simple and complex molecules. It is free of many of the simplifying assumptions that tend to dominate theory and other modeling techniques. So, after making the reasonable extrapolation that computer power will continue to grow at its present rate, the author has little doubt that MD is destined to play an ever-increasing role in both science and engineering.