Many of us have heard about lasers, which produce a special kind of light - but what is special about laser light? Moreover, how can we use laser light to detect and probe a single molecule? Can one single molecule actually be "seen"? Finally, can a single molecule be observed inside a living cell, and what does this tell us? This lecture will provide answers to these questions, and will introduce the audience to a growing new field of science based on using single molecules as tiny, 1 nanometer-sized sources of light. These light sources are being used in diverse areas ranging from single-photon sources to the illumination of complex biological systems in action.