Nickel catalysis offers exciting opportunities for organic synthesis. However, our mechanistic understanding, and our appreciation of catalyst and substrate structure/reactivity relationships has not kept up with the breakneck pace of synthetic innovations. Our research programme is developing a quantitative and systematic understanding of fundamental processes in nickel catalysis. We use a range of techniques from organometallic synthesis, organic synthesis, physical organic chemistry, and computational chemistry to probe these processes, with a focus on oxidative addition. Our work so far has: identified the role of halide abstraction in the reactions of Ni0 complexes with aryl halides, and how this depends on ligand and substrate structure; developed an understanding of oxidative addition to Ni0 complexes with bidentate phosphine ligands such as dppf; identified functional groups that lead to privileged substrates or catalyst inhibitors that can completely shut down cross-coupling reactions; and developed an understanding of the mechanisms of the reactions of alkyl halides with Ni0. This presentation will cover recent research topics, particularly the reactions of alkyl halides with Ni0, and how an understanding of fundamental reactivity can be used to design more efficient cross-coupling reactions.