Who Will Be Appointed as Next Librarian of Congress
The President, in this case, Barack Obama, appoints the Librarian of Congress. Here's the statute about that particular appointment.
Should it be a presidential appointment? Should the next office holder have a degree in Library Science (Mr. Billington did not).
Infodocket has more information on the period of transition, including this:
LC tells us that while no timeline is in place at the moment, President Obama has “roughly” six months to consider nominees for the vacancy. If a new Librarian of Congress is not confirmed by the time of Dr. Billington’s retirement, David Mao, Deputy Librarian, would serve as Acting Librarian of Congress until the time a new leader is confirmed by the Senate. Mao holds both legal and library degrees.