Molecular dynamics has been around since the 60's, and has gained ever increasing popularity as the method of choice for doing computer experiments on molecular systems. Despite the immensity of its forms and applications, the method at its core is built upon rather simple concepts. In this talk, we will look behind the curtain of a generic molecular dynamics simulation, and investigate its main components. We will talk about dynamics of particle systems, forcefields, and integrators, and look at the challenges we face in making the connection between molecular dynamics simulations and the physical world.