The first day of summer in 2025, also known as the summer solstice, will occur on **Saturday, June 21st**. On this day, the Northern Hemisphere will experience the longest period of daylight and the shortest night of the year. The sun will reach its highest point in the sky, marking the official start of the summer season. Many cultures celebrate this day with festivals, outdoor activities, and traditions that honor the sun and the beginning of warmer weather.