Interactive Mathematica simulations with graphical displays of system behavior are an excellent addition to chemical engineering courses. The Manipulate command in Mathematica creates on-screen controls that allow users to change system variables and see the graphical output almost instantaneously. They can be used both in and outside class. More than 400 chemical engineering simulations, developed by a number of authors, are available on the Wolfram site, and they can be used without a Mathematica license.