JEFFREY BROWN:

In recent years, a number of American companies, as many as 22 since 2011, have relocated outside U.S. borders, usually through mergers with or purchases of a foreign company. One impact of changing their business addresses: They're no longer subject to U.S. corporate taxes. It's a process commonly known as a tax inversion.

And Burger King appears to be the latest example. Today, it announced plans to pay some $11 billion for the Canadian restaurant chain Tim Hortons. Burger King will effectively become a Canadian company for tax purposes, though the company denies that was the motive for the move.

Here to tell us about all this is economist Roberton Williams, senior fellow at the nonpartisan Tax Policy Center, a joint venture of the Urban Institute and the Brookings Institution.

And welcome to you.

A tax inversion, it's a phrase that maybe only an economist could like, right, or love. What exactly is it and are we actually seeing more of them?