Covering: 2010 and 2011. Previous review: Nat. Prod. Rep., 2010, 27, 1871 The chemistry and biology of organic natural guanidines are reviewed, including the isolation, structure determination, synthesis, biosynthesis and biological activities of alkaloids, non-ribosomal peptides, guanidine-bearing terpenes, polyketides and shikimic acid derivatives from natural sources.