The first contribution of this book gives an overview on naturally occuring cycling tetrapyrroles. The article describes the four classic tetrapyrrolic structures with their porphyrin, chlorin, bacteriochlorin and corrin skeletons and also novel, interesting structures with unusual biological activities. This review mainly focuses on the occurrence, structure and biological function as well as biosynthesis and aspects of synthesis. The second article deals with the anticancer compound taxol and its semisynthetic analog docetaxel (Taxotere). Taxol was originally isolated in the late 1960's on the basis of its cytotoxity and antileukemic activity, its structure was published in 1971 in a paper that has been cited 1000 times since this publication. The review focuses primarily on the interesting and novel chemistry of taxol that has been discovered over the last eight years.