The party that has the majority of the Senate’s 100 seats elects someone to serve as its spokesperson and leader. The Senate Majority Leader has first recognition rights for any bill that is brought to the floor. This privilege allows him or her to be the first to speak about legislation as well as to have better control over the amendments, substitutions and motions that are considered during debate. The current Senate Majority Leader is Democratic Sen. Harry Reid of Nevada.
http://www.senate.gov/artandhistory/history/common/briefing/Majority_Minority_Leaders.htm#2