The Nasdaq Composite Index rose for a ninth straight day Monday, the longest rally since 2010, while the Standard & Poor's 500 Index was little changed near an all-time high.
The Nasdaq added 0.1 percent, taking it to within 1.7 percent of a record reached 15 years ago. Apple jumped 2.7 percent to an all-time plateau.
The S&P 500 fell less than 1 point to 2,109.66. The Dow Jones Industrial Average dropped 23.60 points, or 0.1 percent, to 18,116.84. About 5.9 billion shares changed hands on U.S. exchanges, 14 percent below the three-month average.
"In this market, there's more just a case of waiting and watching Europe, Greece, OPEC, and waiting to hear from [Fed Chair] Janet Yellen," said Richard Sichel, chief investment officer at Philadelphia Trust Co., which oversees $2 billion. "You put all that together, you get a market that doesn't really have much of a direction. It becomes a much more stocks-specific day."
U.S. stocks last week posted their longest streak of weekly gains since the beginning of December as Greece reached a deal to extend its bailout program and investors speculated the Federal Reserve will keep rates lower for longer. The S&P has advanced 2.5 percent in 2015, trailing all but two of the 24 developed markets tracked by Bloomberg.
The S&P climbed 0.6 percent last week, and the Dow rose to its first record of the year. The Russell 2000 advanced 0.7 percent, also ending at a record.
The Nasdaq has soared 5 percent in nine days to 4,960.97. It is 1.7 percent away from an all-time high reached in March 2000, which preceded a 78 percent drop in the shares.
Apple jumped 2.7 percent to a record after saying it plans to spend $1.9 billion to build data centers in Ireland and Denmark. The project, Apple's biggest European investment, lets it address European requests for data to be stored closer to local users and authorities, while also allowing it to benefit from a chilly climate that helps save on equipment-cooling costs.
Investors will get further clues on the economy's strength this week as Yellen testifies before Congress.
"Yellen meets with Congress this week, and there'll be some Fed watchers looking for direction — whether they're going to raise rates this summer or not," said Bruce Bittles, chief investment strategist at Milwaukee-based RW Baird & Co., which oversees $110 billion.
Strife over Greece's debt was among risks to the U.S. economy cited by Fed officials as an argument for keeping rates low for longer.