The Big Bang Theory is a TV series that aired on CBS from September 24, 2007 to May 16, 2019 for twelve seasons.

Guest Characters

Characters	Guest On	Date	Episode	Crossover Type
George Cooper Jr.	Young Sheldon	May 3, 2018	S11E23: “The Sibling Realignment”	A
George Cooper Jr.	Young Sheldon	May 10, 2018	S11E24: “The Bow Tie Asymmetry”	A
George Cooper Jr., Tam Nguyen	Young Sheldon	October 11, 2018	S12E04: “The Tam Turbulence”	A
George Cooper Sr., George Cooper Jr.	Young Sheldon	December 6, 2018	S12E10: “The VCR Illumination”	A

(Note: George Sr. and George Jr. were mentioned on The Big Bang Theory before they appeared in Young Sheldon, but since Young Sheldon was the first time they were played by actors, I am counting it as their origin point. The episode “The VCR Illumination” has the actors from Young Sheldon appear via an old VHS tape.)

Outgoing Crossovers

Characters	From	Date	Episode	Crossover Type
Arthur “Professor Proton” Jefferies	Young Sheldon	September 25, 2017	S01E01: “Pilot”	A
Arthur “Professor Proton” Jefferies	Young Sheldon	December 21, 2017	S01E09: “Spock, Kirk, and Testicular Hernia”	A
Arthur “Professor Proton” Jefferies	Young Sheldon	January 31, 2019	S02E14: “David, Goliath, and a Yoo-Hoo from the Back”	A
Leonard Hofstadter, Penny Hofstadter, Howard Wolowitz, Raj Koothrappali	Young Sheldon	May 16, 2019	S02E22: “A Swedish Science Thing and the Equation for Toast”	A
Arthur “Professor Proton” Jefferies	Young Sheldon	December 12, 2019	S03E10: “Teenager Soup and A Little Ball of Fib”	A
Arthur “Professor Proton” Jefferies	Young Sheldon	April 16, 2020	S03E20: “A Baby Tooth and the Egyptian God of Knowledge”	A
Arthur “Professor Proton” Jefferies, Amy Fowler	Young Sheldon	November 5, 2020	S04E01: “Graduation”	A
Howard Wolowitz	Young Sheldon	November 18, 2021	S05E07: “An Introduction to Engineering and a Glob of Hair Gel”	A
Amy Fowler	Young Sheldon	March 10, 2022	S05E16: “A Suitcase Full of Cash and a Yellow Clown Car”	A

(Note: While the Young Sheldon episode “A Swedish Science Thing and the Equation for Toast” has appearances by younger versions of the main cast of The Big Bang Theory, later episodes have adult Amy and Howard appear in the Wonder Years style narration as extra voices. )

Spinoffs & Outgoing Cast

Characters	New Show	Date	Episode
Sheldon Cooper, Mary Cooper, Missy Cooper, Connie “Meemaw” Tucker	Young Sheldon	September 25, 2017	S1E01: “Pilot”