A review.The discovery of fluorescent proteins from nonbioluminescent reef corals [reef coral fluorescent proteins (RCFPs)] has greatly expanded the panel of emission wavelengths available for in vivo analyses of cellular events and has opened the door to many new multicolor applications.These RCFP proteins differ not only in their excitation and emission spectra, but also in the time course of fluorescence development, relative brightness, and long-term expression.The unique properties of each RCFP, their expression in mammalian cells, and their use and detection in multiplex applications are described.