BRITE-Constellation, short for “BRIght Target Explorer Constellation,” is a group of six sevenkilogram nanosatellites from Austria, Poland and Canada carrying three-centimeter aperture optical telescopes. The purpose of the mission is to photometrically measure low-level oscillations and temperature variations in stars brighter than visual magnitude 4.0, with unprecedented precision and temporal coverage not achievable through terrestrial-based methods. These stars turn out, for the most part, to be among the most luminous – either massive stars during their whole lifetimes or medium-mass stars at the very end of their nuclear burning phases. Such stars dominate the ecology of the Universe and the current massive ones are believed to represent the lower mass-range of the first stars ever formed (although long gone from the local Universe). Astronomers are eager to measure the variable behavior of luminous stars in order to explore their inner workings in a unique way. BRITE-Constellation will investigate the role that stellar winds play in setting up future stellar life cycles, and will measure pulsations to probe the histories and ages of luminous stars through asteroseismology. Furthermore, as tests with engineering models have demonstrated, it will probably be possible to perform photometry with reduced accuracy of many more stars down to perhaps magnitude 7. The three-axis pointing performance (1 arcminute RMS stability) of each BRITE satellite is a significant advancement by the University of Toronto’s Space Flight Laboratory over anything that has ever flown before on a nanosatellite, and is a critical element that enables this high precision photometry mission. The University of Vienna and FFG/ALR (Austria’s space agency) are financing the development of two satellites and development is nearing completion while the Polish Academy of Sciences is preparing two additional satellites. The Canadian Space Agency is expected to fund soon two satellites in the Constellation. This paper will summarize the science objectives of the mission and describe the progress to date.