Set two years before the events of Clifford the Big Red Dog, the series focuses on when Clifford was a tiny red puppy. Clifford was the runt in a litter of puppies born to the pet dog of Emily Elizabeth's neighbor, Mr. Bradley (who appeared in an episode of the previous cartoon series, "Little Clifford"). He was adopted by Emily Elizabeth before he grew up into a giant red adult dog, forcing the Howard family to move out of their small apartment so Clifford would be able to live comfortably. The series shows Clifford and Emily Elizabeth's life and friends before they moved from the city to Birdwell Island. Clifford's Puppy Days was produced by Scholastic Entertainment and Mike Young Productions and overseas animation services was by Sunwoo Entertainment and Yeson Animation Studios.

• Lara Jill Miller
• Masiela Lusha
• Grey DeLisle
• Henry Winkler
• Julie-Ann Dean