When infrared light is absorbed by molecules, it causes them to vibrate. This paper includes computer animations of molecules vibrating. The animations show two simple molecules (sulfur dioxide and carbon dioxide) vibrating in different modes. In the examples, animated movies show the fundamental vibrational modes of sulfur dioxide and carbon dioxide. Similarly, animations show the composite superposition vibrations. The article explains how scientists calculate which frequencies of infrared light excite specific molecular vibrational modes. The article also provides a great list of references for further study. Finally, this article describes how the excitation of certain molecular vibrations can enhance the chemical reactivity of a molecule. You must pay a fee, or have a subscription to the Journal of Chemical Education to access this Online article. (Install QuickTime to view the animations).