The Summer Solstice is called Litha. This is the day with the longest daylight hours, and depending on the year falls roughly between June 19-22.
This is the time for the rematch between the Oak King and the Holly King, with the Holly King battling his father the Oak King to take his place as ruling the year. He then marries the Goddess, who gives birth to the new Oak King who will battle him come Yule. The old rhyme, Who Killed Cock Robin is about this old tradition of replacing the old worn out king with a younger healthier one. Thus, this battle illustrates the cycle of life. Ritual dramas of this battle are sometimes used in modern Litha celebrations.
Since Litha is a solar holiday, Bonfires are also used.