<P> Once Upon a Time is an American fairy tale drama television series created by Edward Kitsis and Adam Horowitz, who also serve as executive producers alongside Steve Pearlman . It debuted on ABC on October 23, 2011 . The first season introduces a bail bond agent, Emma Swan (Jennifer Morrison) and her birth - son, Henry Mills (Jared S. Gilmore), who discover that a New England town named Storybrooke, Maine is actually a remnant of a parallel world that was cursed by Henry's adoptive mother the Evil Queen / Mayor Regina Mills (Lana Parrilla) and that all the characters from the fairy tales have no memories of who they were, including the parents of Emma: Snow White / Mary Margaret Blanchard (Ginnifer Goodwin) and Prince Charming / David Nolan (Josh Dallas), who sent her to the real world to save their world and break the curse . </P> <P> In February 2018, it was announced the seventh season would serve as the final season of the series . During the course of the series, 155 episodes of Once Upon a Time aired over seven seasons . </P> <Table> <Tr> <Th_colspan="2"> Season </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="4"> Nielsen ratings </Th> </Tr> <Tr> <Th> First aired </Th> <Th> Last aired </Th> <Th> Viewers (millions) </Th> <Th> Viewers rank </Th> <Th> 18--49 rating / share </Th> <Th> 18 - 49 rank </Th> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> October 23, 2011 (2011 - 10 - 23) </Td> <Td> May 13, 2012 (2012 - 05 - 13) </Td> <Td> 11.71 </Td> <Td> 28 </Td> <Td> 4.1 / 10 </Td> <Td> 18 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> September 30, 2012 (2012 - 09 - 30) </Td> <Td> May 12, 2013 (2013 - 05 - 12) </Td> <Td> 10.24 </Td> <Td> 35 </Td> <Td> 3.6 / 9 </Td> <Td> 18 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> September 29, 2013 (2013 - 09 - 29) </Td> <Td> May 11, 2014 (2014 - 05 - 11) </Td> <Td> 9.38 </Td> <Td> 35 </Td> <Td> 3.3 / 8 </Td> <Td> 12 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> September 28, 2014 (2014 - 09 - 28) </Td> <Td> May 10, 2015 (2015 - 05 - 10) </Td> <Td> 8.98 </Td> <Td> 50 </Td> <Td> 3.2 / 7 </Td> <Td> 17 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> 5 </Td> <Td_colspan="2"> 23 </Td> <Td_colspan="1"> September 27, 2015 (2015 - 09 - 27) </Td> <Td> May 15, 2016 (2016 - 05 - 15) </Td> <Td> 6.32 </Td> <Td> 69 </Td> <Td> 2.2 </Td> <Td> 34 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> 6 </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> September 25, 2016 (2016 - 09 - 25) </Td> <Td> May 14, 2017 (2017 - 05 - 14) </Td> <Td> 4.39 </Td> <Td> 105 </Td> <Td> 1.5 / 5 </Td> <Td> 70 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> 7 </Td> <Td_colspan="2"> 22 </Td> <Td_colspan="1"> October 6, 2017 (2017 - 10 - 06) </Td> <Td> May 18, 2018 (2018 - 05 - 18) </Td> <Td> 3.41 </Td> <Td> 120 </Td> <Td> 0.9 </Td> <Td> 115 </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Season </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="4"> Nielsen ratings </Th> </Tr>

How many episodes are in a season of once upon a time