What it is: Nearly $500 billion in automatic tax hikes -- George W. Bush-era rates expire -- and $110 billion in spending cuts in defense and domestic programs will be triggered.

The deadline: Jan. 1; with Congress to return next week, policymakers will have just 49 days to reach consensus.

Why it's happening: The deal was agreed to as a consequence of a supercommittee's failure to settle on a more tailored package of spending cuts and new revenue.