The modern era of organotransition metal chemistry arguably began with the synthesis and characterization of ferrocene in the early 1950’s. For the following twenty years, the field grew substantially in both industrial and academic laboratories. While industry efforts relied on a trial-and-error approach to develop and improve catalysts, academic investigators focused on the structural characterization of new organotransition metal complexes and descriptive studies of their reactions. Although many unusual transformations were discovered during this period, the mechanisms of most of these reactions were poorly understood. In the late 1960’s and 1970’s, a few investigators began to address this dearth of mechanistic understanding. Inorganic chemists who were experts in kinetic investigations afforded one avenue towards gaining insights into organometallic reaction mechanisms. Yet another path was taken by young chemists trained in the physical organic tradition of people like Paul Bartlett, William Doering, Saul Winstein and Jerome Berson. These groups, including mine at Caltech and subsequently UC Berkeley, began to tackle the problem of both discovering new organometallic chemistry and unraveling the mechanisms of these reactions. During the course of our investigations, we made inroads into the discovery and understanding of processes such as alkyne cyclization, nitric oxide migratory insertion and addition of metal nitrosyl complexes to alkenes, organometallic cluster complex formation, alkyne hydroamination, and carbon-hydrogen bond activation. This lecture will provide a personal overview of this work and a historical perspective of our contributions to mechanistic understanding in organotransition metal chemistry during the past 40 years.