First described in the late 1800s, the phenomenon of electric birefringence is becoming increasingly useful as a probe of the solution conformations of proteins and nucleic acids. The birefringence response to a transient electric field is a sensitive indicator of the rotational motions (and hence the physical dimensions) of macromolecules in solution. Recent advances, both in instrumentation and in the efficient production of high-quality biopolymers, have dramatically increased the sensitivity and range of applicability of the method.