The green fluorescent protein (GFP) is a protein that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range. Although many other marine organisms have similar green fluorescent proteins, GFP traditionally refers to the protein first isolated from the jellyfish Aequorea victoria. Jellyfish-derived GFP has been engineered to produce a vast number of useful blue, cyan and yellow mutants, and fluorescent proteins from a variety of other species have also been identified, resulting in further expansion of the available color palette into the orange, red and far-red spectral regions. Together, these highly useful genetically encoded probes are broadly referred to as fluorescent proteins The FP gene can be introduced into organisms and maintained in their genome through breeding, injection with a viral vector, or cell transformation. Green fluorescent protein has transformed biomedical research. Using a gene that carries instructions to make GFP, scientists can attach harmless glow-in-the-dark tags to selected proteins, either in cells in lab dishes or inside living creatures, to track their activity. It’s like shining a flashlight on the inner workings of cells. These days, scientists can track how cancer cells spread, how HIV infections progress and even which male ends up fertilizing a female fruit fly’s egg. These and many other studies that offer insight into human health all benefit from a green, glowing protein first found in a sea creature.