What Is the Difference Between Embezzlement and Theft?

I get this question quite a bit in my practice.

I recently read a piece of news that a nonprofit director was recently charged with $42,000 worth of embezzlement in her role as director of two Yosemite area child centers. While the news is not especially noteworthy, I thought it would be a good chance to explain what exactly embezzlement is and, more specifically, how it differs from theft.