Recent systems for iron-catalyzed C-H functionalization have demonstrated highly promising catalytic performance in a variety of reactions including C(sp²)-H and C(sp³)-H alkylations and arylations, as well as C(sp²)-H amination and annulation reactions amongst others. However, currently available methods only begin to address the potential of iron for catalysis with these bond transformations and numerous challenges and areas for significant improvement remain. These include the current requirement for large amounts of excess nucleophile and oxidant to achieve effective catalysis, the highly variable nature of C-H functionalization reactions, which requires significant re-optimization for each new organic transformation, and the current requirement in nearly all systems for directing groups on the substrate to achieve effective C-H functionalization. Motivation for our research in the Neidig group derives from the hypothesis that a detailed understanding of active catalyst structure, ligand and additive effects, and mechanism can provide the basis for improvements in current catalytic systems, as well as the inspiration for the development of new catalysts and methodologies that will greatly expand the scope and utility of iron for C-H functionalization. Our long-term goals are to develop detailed molecular-level insight into structure, bonding, and reactivity across the spectrum of iron-catalyzed C-H activation systems in order to form the basis for the design and development of new iron catalysts with improved performance. This includes more atom efficient methods, alternative reaction manifolds to enable complementary reaction methods, the development of universal supporting ligands for effective catalysis across a broad range of C-H functionalizations and, ultimately, C-H functionalization reactions that are effective across diverse substrate classes in the absence of directing groups on the substrate.