Book excerpt: Carbocyclic and Heterocyclic Cage Compounds and their Building Blocks is the first independent Supplement in the series. The collection of essays presented is very much at the forefront of research in this active area and the topics discussed complement and evolve from the more general treatment in earlier volumes of the Series. Furthermore it was appropriate to produce a collection of work at the cutting edge of the field, where progress in heterocyclic cage compounds are discussed together in a single volume, thus avoiding the organic versus organometallic barriers in an effort to raise more awareness concerning their similarities and differences. Since phosphaalkynes serve as building blocks for a host of phosphorus-carbon cage compounds discussion of the versatile chemistry of phosphaalkynes is relevant. Likewise, discussion of the versatile chemistry of phosphaalkenes is appropriate since they function as synthetic precursors to phosphaalkynes and are the products of electrophilic addition to phosphaalkynes.