GFP was first isolated and characterized from a species of jellyfish during the 1960s and 70s, but it's potential for laboratory use was not explored until the early 1990s. Since then it has been widely used in fluorescence microscopy, especially in the field of cellular biology. Notably, since it is non-toxic it allowed scientists to incorporate it into living systems. The nucleotide sequence for GFP can be spliced into the genome under the same regulatory sequence, or promoter, as a given protein of interest. By doing this, expression of the protein of interest coincides with expression of GFP, which can be easily detected. This general technique can be applied to show which cells are expressing a certain protein, or it can be used to study protein localization, transport and other time-sensitive processes that occur in living cells.
Numerous GFP derivatives have been generated by mutating the original wild-type sequence to alter the protein's spectral characterstics. Many laboratories now use not only green fluorescent protein, but also cyan, blue, and yellow as well. GFP has even found it's way into numerous animals which are commercially available, such as GloFish.