From the polarization of light in the sky, to the Earth's magnetic field-- we are surrounded by a universe of invisible cues. Organisms as diverse as bacteria, birds, insects, and fish rely on these hidden stimuli to navigate, communicate and forage. We will explore the organization and function of the extraordinary sensory systems that allow organisms to detect these cues. We will consider both the environmental and evolutionary context within which these sensory systems must function, and the history behind key discoveries in each system. Readings will include primary scientific literature and book chapters. Students will give in-depth presentations on a pre-selected topic, and discuss readings each week in a journal club-style format.