Beltane or Bealtaine is the Gaelic May Day festival, marking the beginning of summer. It is traditionally held on 1 May, or about midway between the spring equinox and summer solstice. Historically, it was widely observed in Ireland, Scotland, and the Isle of Man. In Ireland, the name for the festival in both Irish and English is Bealtaine. In Scottish Gaelic it is called Latha Bealltainn, and in Manx Gaelic Laa Boaltinn/Boaldyn. Beltane is one of the four main Gaelic seasonal festivals—along with Samhain, Imbolc, and Lughnasadh—and is similar to the Welsh Calan Mai.

Summer is the hottest and brightest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, daylight hours are the longest and darkness hours are the shortest, with day length decreasing as the season progresses after the solstice. The earliest sunrises and latest sunsets also occur near the date of the solstice. The date of the beginning of summer varies according to climate, tradition, and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa.