For plants, the sensing of light in the environment is as important as vision is for animals. Fluctuations in light can be crucial to competition and survival. One way plants sense light is through the phytochromes, a small family of diverse photochromic protein photoreceptors whose origins have been traced to the photosynthetic prokaryotes. During their evolution, the phytochromes have acquired sophisticated mechanisms to monitor light. Recent advances in understanding the molecular mechanisms of phytochromes and their significance to evolutionary biology make possible an interim synthesis of this rapidly advancing branch of photobiology.