The letter is already posted on the foundation's Web site. The contents are similar to what Gates has been saying in recent speeches and interviews: don't let the economy throw off the momentum of fighting disease and poverty.

Gates discusses the economic crisis here. He says his foundation lost 20 percent of its assets in 2008. That figure could be nearly $8 billion. The foundation had about $39 billion in assets at the end of 2007, according to its annual report.

"I never thought I would say losing 20 percent is a reasonable result, but it is better than most endowments because so many asset classes went down by more than 20 percent in 2008," Gates writes.

Nevertheless, the foundation will be spending more this year than it did last year ... $3.8 billion, about 7 percent of its assets, compared to $3.3 billion last year.

He quotes from John Maynard Keynes' essay "The Great Slump of 1930," drawing parallels to today. In "five to ten years, I am very optimistic that these problems will be behind us."

Gates says foundation needs the "innovation power" of business; next year he hopes to show examples of where "creative capitalism" has made a difference.

"The common sense of the business world, with its urgency and focus, has strong application in the philanthropic world," he writes. And yet, he's sure that he'll "make mistakes in over-applying some elements from my previous experience and will need to adjust."

On health, it's interesting that Gates points to research that shows better health is linked to smaller families, addressing an argument made by some that reverses that notion, claiming that population control will improve health in developing countries.

On technology he says it's a personal passion, and that things like building health clinics or roads.. "are better left to governments."