Legislation that has passed both houses of Congress is sent to the President for his approval. The President has 10 days to sign or veto the bill.

If the President vetoes the bill it is returned to Congress with his objections and may be reconsidered. A two-thirds affirmative vote by both the House and Senate overrides the President's veto and the bill becomes law without his signature.

If the President does not act within ten days the legislation becomes law automatically -- unless Congress has adjourned. If Congress has adjourned, preventing the President from returning the bill, the legislation dies in a "pocket veto".

A bill becomes law on the date it is signed unless a different effective date is specified.

(Source: How Our Laws are Made)