Reuters [reuters.com] and Yahoo Finance [yahoo.com] report that the Dow 30 [wikipedia.org] NASDAQ [wikipedia.org] and S&P 500 [wikipedia.org] stock indexes all reached record high levels on Monday. According to Yahoo this last occurred in 1999.
Reuters cited as possible factors speculation that the central bank will not soon raise interest rates, rising oil prices due to speculation that oil producers may cut production, and a Bureau of Labor Statistics report [bls.gov] issued earlier in the month.