The difficulties students face with organic reaction mechanisms have been the subject of much research in chemical education however, no concept inventory has been reported in this area. The development of a concept inventory would be useful for the large-scale assessment of students’ understanding of concepts pertinent to developing proficiency in reaction mechanisms. The first step in the design of such an inventory is identifying the pertinent concepts. In phase 1 of this study, open-ended interviews were carried out with organic chemistry instructors (N = 11) in order to ascertain their opinions on pertinent concepts for developing proficiency in reaction mechanisms. Phase 2 of the study consisted of a national survey of organic chemistry instructors (N = 183) to explore the general consensus regarding the concepts identified in phase 1. The results yielded 10 concepts identified by experts to be pertinent to reaction mechanisms. The general consensus among organic chemistry instructors is that the topic of reaction mechanisms is important to the study of organic chemistry, but students have difficulty understanding the meaning of the curved-arrow notation. Future work will include the design and development of a concept inventory based on these pertinent concepts.