My goal in writing this text is to help advanced undergraduates and beginning graduate students learn key topics in organic chemistry that often don't come up in your Organic I and II classes. So, you can think about this as an Organic III text. My focus is on key reaction types that enable the construction of complex organic molecules: pericyclic reactions, transition metal catalyzed reactions, rearrangements, fragmentations, radical reactions, and carbene reactions. I hope that this text is a resource that helps you understand the mechanisms of these reactions and enables you to use these reactions in your own syntheses. I have provided a variety of mechanism and synthesis problems to help you practice these skills and make them your own. One of the main goals in my Organic Synthesis class is to engage deeply with current papers from the literature. I hope you will do the same and that this text will help you understand some of the concepts and reactions that often go unspoken in publications. Front Matter 1: Pericyclic Reactions 2: Transition Metal Catalyzed Carbon-Carbon Bond Forming Reactions 3: Neighboring Group Participation, Rearrangements, and Fragmentations 4: Radical Reactions 5: Carbene Reactions Back Matter Thumbnail: Work up of a reaction sketched on fume hood sash glass. (Unsplash License; Chromatograph via Unsplash )