Songfacts®:

• This was the first hit song written by Paul Evans, who had a few hits of his own and went on write "Roses Are Red (My Love)" for Bobby Vinton. Evans told Songfacts: "I was young. I was 19 or 20. 'When' was written by a co-writer [Jack Reardon]. I used to go into New York City. I lived in the suburbs out in Queens, so I would take a bus and the train into the city, and I would write with two or three writers a day - it was our job to write songs. It was two different guys in most cases, just sitting around, fooling around playing songs. Somewhere along this road a new song began.
  
  But when specifically the Everly Brothers were around, everybody wanted the Everly Brothers. They were superstars. So we wrote a song for the Everly Brothers. It was 'When,' but the Everly Brothers were almost impossible to get if you weren't Boudleaux Bryant and his wife Felice. So we brought the song up to Decca Records, and the demo was just my guitar, me singing, and my co-writer singing a harmony line. Once through we sang the song. We got the Kalin Twins to do it because Decca, who did they think of when they heard a duet on a demo? They thought of a duet, that's just the way it was in the business at the time.
  
  We did not write it as a personal experience. We tried. We wrote it because we wanted to write a song that we could get recorded. We were writers. I brought my lunch in in a bag. I left, taking a year off of school. I was going to Columbia at college and had a scholarship that had just turned into a full scholarship there for me, but I wanted to try the music business. I did promise myself - and I must say, my mother and father - that if I didn't have some kind of success in that one year, that I would go back to school, and I would have. Just then, The Kalin Twins record came along, and the joke is - and it's true - my mother, when she'd get on the phone before I had my big hit, people would say, 'How's Paul doing?' And she would say, 'Mmph, Paul, mmmm, left college, and he's going to be a songwriter. A singer. Mmph.' And then, after when my mother would pick up the phone and they'd say, 'How's Paul doing? she's say, 'Oh! Maybe you heard his newest hit, the Kalin Twins record 'When'!' It was really fun for me."
• The Kalin Twins were the first act with twins to make the Top 10 in the US or UK. The next group to do it was The Bee Gees, whose first American Top 10 was "I've Gotta Get A Message To You" in 1968. In the UK, it was the #1 "Massachusetts" in 1967.