The track is about various different activities that take place in the summer. Wiseman told the story of the song to The Boot
: "Steve was in town from London. We had about three days to write, so we were really taking advantage of our time. We'd go til 1:00 or 2:00 in the morning... until we dropped!
We were writing 'My Old Friend' [for Tim McGraw], but we were trying not to write a ballad so we kept trying not to write that particular song. Finally around midnight, we took a break from writing 'My Old Friend' and went out on the back steps of my office. It was that first night when it stays warm, and you can smell the grass growing. I walked outside and was like, "Man... summertime! Smell that!" It was that first warm night of summer. It was great.
That next day, I was driving in to write with Steve. For whatever reason, I kept going, "Summertime! Summertime!" It was sticking in my head. We got to the office, and I pulled up a drumbeat and started saying it to the beat. I didn't want to call it 'Summertime,' because you want to come up with a little better of a title than that, but it just kept coming back to 'Summertime.'
I'm from Mississippi, so I'm a kid from the South. Summertime was always the start of the year for me, and it still is. I look at my year starting not in January, but in June when school is letting out. If I'm going to be associated with a season, I'd rather it be summertime than try to write another Christmas song or something!"