The pyrolysis of styrene to benzene and acetylene was studied using quantum chemical methods. The pyrolysis of styrene might proceed by three different mechanisms: concerted decomposition to benzene and vinylidene; concerted decomposition to benzene and acetylene; and decomposition via an intermediate. An intermediate similar to [4.1.0]-7-methylene cycloheptadiene was found, suggesting that the pathway via the [4.1.0]-7-methylene cycloheptadiene might be a two-step reaction. Comparisons to previous experimental investigations were also presented. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).