The emission of light by living organisms is a fascinating process. The genetic system required for luminescence in the bacterium Photobacterium (Vibiro) fischeri is the lux operon. This operon contains a gene for luciferase (the enzyme that catalyzes the light-emitting reaction) and genes for enzymes which produce the luciferins (which are the substrates for the light-emitting reaction.). In this exercise, students create a luminescent population of bacteria by introducing into E.coli a plasmid that contains this lux operon. The success of the transformation is readily apparent since the E.coli colonies that take up this plasmid glow in the dark as shown below. The simple procedure can be carried out during a single 1-1.5 hour laboratory session. Sufficient sterile materials are provided for sixteen platings and the experiment is designed for 8 groups of students.