The song was written and composed by duo partner Chad Stuart (Jeremy Clyde made few contributions to Stuart's and his repertoire) with Clive Metcalfe and Keith Noble. Like Stuart's and Clyde's breakthrough selection in duo partnership, "Yesterday's Gone," "A Summer Song" is a reminiscence of a summer romance. However, "A Summer Song" eschews the "Merseybeat" sound of "Yesterday's Gone" in favor of a gentler folk-influenced arrangement, with the lyrics also being wistful in tone. Stuart would recall, on The Steel Pier Radio Show, that his "A Summer Song" collaborators, Clive Metcalfe and Keith Noble, were themselves a musical duo with whom he and Clyde had become friendly, and that "A Summer Song" was written and composed in Stuart's flat in London: "We were sitting around jamming on four chords and we came up with 'A Summer Song.'" "We never thought 'Summer Song' could possibly be a single," he recalled another time. "It was just a pretty, romantic song. Or so we thought...you never can tell, can you?"