The Main Cast:
* Phineas Flynn: The inventive, energetic older brother. Voice by Vincent Martella.
* Ferb Fletcher: The quiet, resourceful younger brother. Voice by Thomas Sangster.
* Candace Flynn: Their older sister who is obsessed with busting them for their crazy inventions. Voice by Ashley Tisdale.
* Perry the Platypus: Phineas and Ferb's pet platypus, who secretly works as a secret agent for the O.W.C.A. (Organization Without a Cool Acronym). Voice by Dee Bradley Baker.
* Dr. Heinz Doofenshmirtz: The evil scientist who lives across the street, constantly trying to take over Tri-State Area. Voice by Dan Povenmire.
* Isabella Garcia-Shapiro: Phineas' crush, a member of the Fireside Girls. Voice by Alyson Stoner.
* Buford Van Stomm: The tough and somewhat dimwitted bully. Voice by Bobby Gaylor.
* Baljeet Tjinder: Phineas and Ferb's intelligent and often-nervous friend. Voice by Maulik Pancholy.
* Jeremy Johnson: Candace's crush, a popular boy. Voice by Mitchel Musso.
* Phineas and Ferb's Mom: A loving and supportive mother. Voice by Caroline Rhea.
* Phineas and Ferb's Dad: A laid-back and often oblivious father. Voice by Richard O'Brien.
Recurring Characters:
* Major Monogram: Perry's boss at O.W.C.A. Voice by Jeff "Swampy" Marsh.
* Agent P: Perry's secret agent codename.
* Stacy Hirano: Candace's best friend, who is often skeptical of Candace's attempts to bust Phineas and Ferb. Voice by Kelly Hu.
* The Fireside Girls: A group of girls who are always eager to help Phineas and Ferb. Voice by Alyson Stoner, Ashley Tisdale, and others.
* The Evil Sidekick: Doofenshmirtz's bumbling assistant. Voice by Dee Bradley Baker.
* Vanessa Doofenshmirtz: Doofenshmirtz's teenage daughter, who is usually embarrassed by her father's villainous antics. Voice by Olivia Olson.
* Norm: Doofenshmirtz's robot butler.
* The Narrator: A mysterious voice who narrates many of the episodes. Voice by Dee Bradley Baker.
This list covers most of the main characters, but Phineas and Ferb is known for its large ensemble cast and its many recurring characters, so there are many more characters that could be listed!