The diterpenoid alkaloids, with an intriguing chemistry and numerous varied bioactivities, constitute the largest and most complicated group of terpenoid alkaloids. Among them, the C19-diterpenoid alkaloids have attracted extensive and lasting attention from researchers. This chapter with 1075 references systematically summarizes the past 30 years of studies on the C19-diterpenoid alkaloids, covering the classification and distribution, biogenesis and biosynthesis, applications in the phytochemotaxonomy of Chinese Aconitum L., spectral properties (1H and 13C NMR, MS), X-ray crystallographic analysis, chemical reactions and chemical conversions (as a continuation of Volume 42 of this treatise), and pharmacological activity of this important group of alkaloids. This review on the C19-diterpenoid alkaloids, in combination with two previous reviews in this treatise (C20-diterpenoid alkaloids, Volume 59, and C18-diterpenoid alkaloids, Volume 67), will present readers with a complete and updated profile of the diterpenoid alkaloids. The only exception is the description of the total syntheses of the diterpenoid alkaloids, which will be summarized in a subsequent individual chapter.