Further reading: Yes I Will at Wikipedia.
Of the two writers, Gerry Goffin (1939–2014) is the better known, as songwriting partner with his wife Carole King.
Russ Titelman (b. 1944), a singer-guitarist-composer who was an early associate of Phil Spector, became known as a producer for the likes of Eric Clapton, Little Feat, George Harrison, and Brian Wilson. He also wrote a number of choice but often overlooked songs in the 60s, notably the sublime What Am I Gonna Do With You (Hey Baby), written with Gerry Goffin and recorded by The Inspirations, The Chiffons, Lesley Gore and Skeeter Davis.
See also Little Pattie – Little Things Like That, another Titelman co-composition.
Further reading: 1. Some Russ Titelman compositions are listed in a Spectropop post by Declan Meehan, for whom Titelman is one of the greatest unsung co-writers or writers… especially in the girl group genre. 2. Again at Spectropop, Mike Edwards also lists some of Titelman’s songs and co-writers. 3. Annotated playlist from a Spanish radio show dedicated to Titelman productions and compositions (at Flor de Pasion). 4. Timothy White interviews Russ Titelman (Billboard, 1996, reprinted at Spectropop.com
Yes I Will with a different title, on their first album The Monkees (1966).