Fluorescent proteins are genetically encoded, highly versatile reporters useful for monitoring various aspects of recombinant protein production. In addition to the widely popular green fluorescent protein (GFP) from Aequorea victoria, a variety of other fluorescent proteins have been discovered that display a wide range of spectral properties. Synthetic variants have also been developed to overcome limitations associated with their wild-type counterparts. Having a large repertoire of fluorescent proteins with diverse traits opens new opportunities for rapid monitoring and optimization of recombinant protein production.