<Table> <Tr> <Th_colspan="2"> United States Senate </Th> </Tr> <Tr> <Td_colspan="2"> 115th United States Congress </Td> </Tr> <Tr> <Td_colspan="2"> Seal of the U.S. Senate </Td> </Tr> <Tr> <Td_colspan="2"> Flag of the U.S. Senate </Td> </Tr> <Tr> <Th_colspan="2"> Type </Th> </Tr> <Tr> <Th> Type </Th> <Td> Upper house of the United States Congress </Td> </Tr> <Tr> <Th> Term limits </Th> <Td> None </Td> </Tr> <Tr> <Th_colspan="2"> History </Th> </Tr> <Tr> <Th> New session started </Th> <Td> January 3, 2017 (2017 - 01 - 03) </Td> </Tr> <Tr> <Th_colspan="2"> Leadership </Th> </Tr> <Tr> <Th> President of the Senate </Th> <Td> Mike Pence (R) Since January 20, 2017 </Td> </Tr> <Tr> <Th> President pro tempore </Th> <Td> Orrin Hatch (R) Since January 6, 2015 </Td> </Tr> <Tr> <Th> Majority Leader </Th> <Td> Mitch McConnell (R) Since January 3, 2015 </Td> </Tr> <Tr> <Th> Minority Leader </Th> <Td> Chuck Schumer (D) Since January 3, 2017 </Td> </Tr> <Tr> <Th> Majority Whip </Th> <Td> John Cornyn (R) Since January 3, 2015 </Td> </Tr> <Tr> <Th> Minority Whip </Th> <Td> Dick Durbin (D) Since January 3, 2015 </Td> </Tr> <Tr> <Th_colspan="2"> Structure </Th> </Tr> <Tr> <Th> Seats </Th> <Td> 100 </Td> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> Political groups </Th> <Td> <P> Majority (51) </P> <Ul> <Li> Republican (51) </Li> </Ul> <P> Minority (49) </P> <Ul> <Li> Democratic (47) </Li> <Li> Independents (2) caucusing with the Democrats </Li> </Ul> </Td> </Tr> <Tr> <Th> Length of term </Th> <Td> 6 years </Td> </Tr> <Tr> <Th_colspan="2"> Elections </Th> </Tr> <Tr> <Th> Voting system </Th> <Td> First - past - the - post; nonpartisan blanket primary with a majoritarian second round in 3 states . </Td> </Tr> <Tr> <Th> Last election </Th> <Td> November 8, 2016 (34 seats) </Td> </Tr> <Tr> <Th> Next election </Th> <Td> November 6, 2018 (33 seats) </Td> </Tr> <Tr> <Th_colspan="2"> Meeting place </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Td_colspan="2"> Senate chamber United States Capitol Washington, D.C., United States </Td> </Tr> <Tr> <Th_colspan="2"> Website </Th> </Tr> <Tr> <Td_colspan="2"> senate.gov </Td> </Tr> <Tr> <Th_colspan="2"> Constitution </Th> </Tr> <Tr> <Td_colspan="2"> United States Constitution </Td> </Tr> </Table> <Tr> <Th_colspan="2"> United States Senate </Th> </Tr>

How many seats are in the united states senate