Anyone paying attention to financial markets in recent months knew that the Federal Reserve’s management of the economy was perhaps the single most important question on the minds of investors.

The Fed, of course, has been raising interest rates, including four increases last year, which unnerved many investors. These days, though, the focus has shifted to what the central bank will do with another tool it previously used to stoke economic growth.

As part of its campaign to rescue the economy after the 2008 financial crisis, the Fed bought enormous quantities of bonds issued or guaranteed by the federal government. Now the question is how quickly, and by how much, it will shrink that pile.

On Wednesday, the Fed left rates unchanged and signaled that it could slow its bond sales if economic and financial conditions change. Investors cheered, with the S&P 500 rising about 1.5 percent. The index is up nearly 7 percent this year.