[Truncated abstract] This study was carried out to investigate the teaching and learning processes occurring in the topic of reaction mechanisms in three tertiary level organic chemistry courses and focussed on investigating perceptions about the importance of teaching and learning about reaction mechanisms and about the difficult aspects of the topic .... In the organic chemistry courses under investigation, students achieved many of the explicitly stated aims that their lecturers identified. The students rarely achieved implicit outcomes anticipated by the lecturer. Lecturers demonstrate a tendency to use particular structural representations when discussing certain types of reaction process. The study identified that students commonly use these same types when working through particular reaction processes. In addition, it was found that the use of a particular structure could cue students into thinking about only one type of reaction process taking place in a given reaction. The use of language that is consistent with a consideration of only single reaction particles was also commonly observed in lectures. While this can be adequate in some circumstances, other aspects of reaction processes are better considered in terms of multiple reaction particles ... The project proposes an integrated model, which takes into account the many levels (macroscopic, single particle molecular, multiple particle molecular and intramolecular) involved when describing reaction processes. It is felt that a consideration of the levels discussed in this model is useful when teaching and learning about reaction mechanisms.