Here we report on the isolation, structure elucidation, biosynthesis, and biological properties of tubulysins A–I (Mep = N-methyl pipecolic acid, Ile = isoleucine, Tuv = tubuvaline, Tut/Tup = tubutyrosine/tubuphenylalanine). Two different species of myxobacteria, Archangium gephyra and Angiococcus disciformis, were identified to produce tubulysins, and the compounds were isolated by multistep chromatography from culture extracts. A. gephyra produces 2–4 mgL⁻¹ of tubulysin A and minor components tubulysins B, C, G, and I (characterized by a p-hydroxyphenyl residue), while A. disciformis produces 0.5 mgL⁻¹ of the phenyl analogues tubulysins D, E, F, and H. Structure elucidation of tubulysins by NMR spectroscopy was seriously complicated by signal broadening and lack of signals for certain atoms, which was addressed by a biosynthetic labeling study: feeding with 13C-enriched presumed polyketide precursors indicated incorporation of three acetate units and three methyl groups from methionine, facilitating 13C NMR assignment and enabling structure elucidation of tubulysin A (C₄₃H₆₅N₅O₁₀S) via 1D and 2D NMR as a linear tetrapeptide of N-methyl pipecolic acid (Mep), isoleucine (Ile), tubuvaline (Tuv), and tubutyrosine (Tut). In tubulysins D, E, F, and H, Tut is replaced by tubuphenylalanine (Tup). All tubulysins share a 5-acetoxy residue in Tuv, but the N-acyloxymethyl substituent varies in size (3-methylbutyrate in tubulysins A and D, acetate in H and I). The N-acyloxymethyl substituent is a formaldehyde N,O-acetal, and formaldehyde was liberated upon acidic hydrolysis.