WASHINGTON, Dec. 2 -- Dec. 3 is Giving Tuesday, a global movement to unleash the power of people and organizations to transform their communities and the world. It was created in 2012 as a simple idea: a day that encourages people to do good.

"We are a nation of generous people," said Barbara Stewart, CEO of the Corporation for National and Community Service, the federal agency for volunteering and service. "Giving to organizations you care about is an important part of our role as citizens. During this season of thanks and giving, we encourage our fellow citizens to make a commitment to volunteer this holiday season and all year long."

Many have answered the call to service. According to the latest "Volunteering in America" report, prod...