This song has a very joyful and upbeat melody, but the lyrics are quite painful, as the singer has lost her man and is left with just memories. The song was written by Terry Cashman and Gene Pistilli. Terry Cashman
told Songfacts in a 2009 interview: "Gene actually worked for me. One day he came into the office, and he had this chord progression he came up with. Most simple rock and roll chord progressions in the key of G would be G to E minor to A minor to D. And Gene came in with a change which was instead of going from G to E minor, he went to E major, and instead of going to an A minor – the typical rock and roll kind of thing – he went to an A major, so it made it sound different. And when he played it for me, I started singing this melody to it. And you know, it made me think of a girlfriend that I had a few years before. We used to walk in the park on Sundays, and that whole story became the idea for the song because she left him, and the love affair was over, that Sunday, that special day would never be the same. We wrote the song very quickly. That song Gene and I wrote and Tommy West helped us with the demo, and we did a really, really good demo of the song.
I was the head of the publishing company, so my job was to take the songs that we had made around to the various producers. I sent it to Lou Adler at Dunhill Records, which was associated with ABC for the Mamas and Papas. He said, 'Hey, this is a great song.' But John Philips, is doing mostly his own songs right now. So, okay, fine. The Left Banke sounded to me also like a group that could do this song, but they passed on it. And then with nobody in mind I went to a producer named Jerry Ross, who was a very hot producer. He had produced 'Apples, Peaches, Pumpkin Pie' for Jay and the Techniques, and '98.6' with an artist called Keif. So I played him the demo, and after about 16 bars he took the needle off the vinyl, and he said, 'Has anybody else heard this song?' And I said, 'Well, Lou Adler turned it down for Mamas and Papas, and Left Banke turned it down.' And he said, 'Well, don't play it for anybody else. I have this great group.' And he played me a demo of a record that Spanky & Our Gang had done, and they had all these vocal harmonies. A couple of months later he cut the song, and it was a smash hit. It was something that really put me on the map in terms of the music industry."