<P> The Flash is an American action television series developed by Greg Berlanti, Andrew Kreisberg, and Geoff Johns, airing on The CW . It is based on the DC Comics character Barry Allen / Flash, a costumed crimefighter with the power to move at superhuman speeds . It is a spin - off from Arrow, existing in the same fictional universe . The series follows Barry Allen, portrayed by Grant Gustin, a crime scene investigator who gains superhuman speed, which he uses to fight criminals, including others who have also gained superhuman abilities . The Flash was renewed in March 2016 for a third season, which premiered on October 4, 2016 . On January 8, 2017, The CW renewed the series for a fourth season, which premiered on October 10, 2017 . As of December 5, 2017, 78 episodes of The Flash have aired . </P> <Table> <Tr> <Th_colspan="2"> Season </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="2"> Nielsen ratings </Th> </Tr> <Tr> <Th> First aired </Th> <Th> Last aired </Th> <Th> Rank </Th> <Th> Average viewership (in millions) </Th> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 23 </Td> <Td_colspan="1"> October 7, 2014 (2014 - 10 - 07) </Td> <Td> May 19, 2015 (2015 - 05 - 19) </Td> <Td> 118 </Td> <Td> 4.62 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 23 </Td> <Td_colspan="1"> October 6, 2015 (2015 - 10 - 06) </Td> <Td> May 24, 2016 (2016 - 05 - 24) </Td> <Td> 112 </Td> <Td> 4.25 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> 23 </Td> <Td_colspan="1"> October 4, 2016 (2016 - 10 - 04) </Td> <Td> May 23, 2017 (2017 - 05 - 23) </Td> <Td> 120 </Td> <Td> 3.50 </Td> </Tr> <Tr> <Td> </Td> <Td_colspan="1"> </Td> <Td_colspan="2"> TBA </Td> <Td_colspan="1"> October 10, 2017 (2017 - 10 - 10) </Td> <Td> TBA </Td> <Td> TBA </Td> <Td> TBA </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Season </Th> <Th_colspan="2"> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th_colspan="2"> Nielsen ratings </Th> </Tr>

When does season 4 episode 1 of the flash air