MR simulations based on the Bloch Equations are of high educational value. Further, they serve as essential tools in MRI method development, e.g. for MR sequence design and protocol optimization or generating ground truth data for image reconstruction and post-processing algorithms. This lecture provides insight into practical implementation of computer simulations based on classical MR physics. Analytical solutions versus numerical implementations will be discussed. Based on pictorial examples, an introduction to various MRI simulator software packages will be given. The JEMRIS simulation environment will serve for most of the examples shown in this lecture.