  Years to decade-long cyclic period changes have been observed in many classes
of close binaries. A common explanation invoked for these cyclic period changes
is the gravitational influence of an unseen third body upon the close binary
pair. The effects of an unseen third body must be strictly periodic, and not
all of these observed period variations match this prediction. Douglas Hall
noted almost 20 years ago that Algol binaries with cyclic period changes always
had a convective, rapidly rotating secondary star. This secondary star has the
seeds for a powerful magnetic dynamo, and the suggestion was made that magnetic
activity was the cause of the observed cyclic period changes.
  In this paper I will review the observational evidence for a magnetic cycle
driving the observed cyclic period changes. I will also discuss the theoretical
framework which now exists to explain how the magnetic cycle can alter the
orbital period of a close binary. I will close by discussing an ongoing
observational effort to test the predictions of the magnetic activity-cyclic
period change connection.
