Bioluminescence imaging (BLI) is a technology that allows for the noninvasive study of ongoing biological processes in small laboratory animals. Bioluminescence is the process of light emission in living organisms. Bioluminescence imaging utilizes native light emission from one of several organisms which bioluminesce. The three main sources are the North American firefly, the sea pansy (and related marine organisms), and bacteria like Photorhabduss luminescens and Vibrio fischeri. The DNA encoding the luminescent protein is incorporated into the laboratory animal either via a viral vector or by creating a transgenic animal. Common applications of BLI include in vivo studies of infection (with bioluminescent pathogens), cancer progression (using a bioluminescent cancer cell line), and reconstitution kinetics (using bioluminescent stem cells).