Fluorescence of marine organisms has fascinated researchers since the early twentieth century. The successful application of the green fluorescent protein (GFP) from the jellyfish Aequorea victoria in 1994 as genetically encoded marker resulted in a massive increase in interest for naturally fluorescent proteins. Methods are now established that allow the fast isolation of new genes encoding GFP-like proteins from marine creatures, resulting in an impressive array of glowing proteins with different biochemical and optical properties. Protein engineering has been applied to render natural variants into advanced optical tools for live cell imaging, promoting studies of protein localization and movement, gene activity, sensing of intra- and extracellular condition, and tracking of whole cells and organisms. Finally, photoactivatable proteins were discovered that enable pulse-chase experiments and live cell imaging of proteins with a resolution beyond the diffraction barrier of optical microscopy. Phylogenetic sequence analyses revealed interesting details about the molecular evolution of these proteins including the convergent evolutio ... mehrn of colors. Marine organisms, especially corals, still harbor a huge number of GFP-like pigments, the majority of which are yet to be studied. Consequently, further important discoveries of useful marker proteins can be expected in the future.