Janet Yellen to the rescue?

When Janet Yellen speaks, markets listen.

With stocks sliding and geopolitical tensions flaring, the bulls hope her recent sway over U.S. stocks continues.

The Federal Reserve kicks off a two-day policy meeting this week, capped by Ms. Yellen's first press conference as head of the central bank on Wednesday. Market watchers will closely monitor her thoughts on stimulus–most anticipate the Fed will dial back its bond-buying program by another $10 billion a month–and any changes to forward guidance.