The scientific motivation driving the work in Professor Broadbelt’s research group is unraveling complexity in reacting systems. They recognize that macroscopic observations are linked to microscopic phenomena, and analysis spanning these regimes provides the best opportunity for fundamental understanding and development of novel engineering strategies. The systems that they study, however, are sufficiently complex that the atomic-scale events leading to the observed behavior are obscured. They concentrate their efforts in three main topical areas using a combination of experiment and theory. Reaction systems that they model may consist of thousands of reactive intermediates and molecules and thus are too large for models to be developed without automated computer tools. Polymeric systems that they study require description of transformations of high molecular weight chains and evolution of low molecular weight products. Catalytic and biocatalytic systems that they investigate demand quantification of the interaction energies between numerous species and complex catalytic environments. They therefore develop capabilities to facilitate quantitative analysis and description of complex systems at the macroscopic level, and they devise strategies and apply tools for probing and quantifying molecular-level events.