Summer, the season of the year occurring between spring and autumn. Astronomically, summer in the Northern Hemisphere lasts from about June 21 to September 23; in the Southern Hemisphere, from about December 22 to March 21. The exact beginning of the season is marked by the summer solstice, when the sun reaches its highest point overhead.

Summer brings the warmest weather of the year to those regions having four distinct seasons. Because of the time needed for the hemisphere to regain the heat lost during winter, the warmest period of summer does not coincide with the solstice, but occurs several weeks afterward.