Who has the authority to sign bills into law?

The authority to sign bills into law resides with the President. This power is established in the U.S. Constitution, specifically in Article I, Section 7, which outlines the legislative process. After a bill is passed by both the House of Representatives and the Senate, it is sent to the President. The President can then take one of several actions: they can sign the bill, thereby enacting it into law; they can veto it, sending it back to Congress; or they can take no action, in which case the bill may become law automatically after a certain period, unless Congress adjourns.

The other options reflect roles in the legislative process but do not include the signing authority. The Vice President serves as the President of the Senate but does not have the power to sign bills into law. The Senate and the House of Representatives are responsible for debating, amending, and passing legislation, but once a bill is passed, it is solely the President's role to sign it into law or veto it. Thus, the President is the pivotal figure in this crucial step of the legislative process, confirming why this answer is correct.