Although they are from two different networks but NBC's "The Office" and FOX's "Glee" are on mutual term. The popular TV series will do sort of a crossover later this season when the staff of Dunder Mifflin gather to watch an episode of "Glee".
It looks like it won't be a small bit like when the staff watched a pirated movie starring Jack Black in the episode airing after Super Bowl XLIII. According to Entertainment Weekly, the "entire upcoming episode", which air date is still unknown, is dedicated to "getting together to watch" the musical show. However, no cast from "Glee" would actually be present at the office.
This Thursday, October 7, "The Office" will air an Andy-centric episode called "Andy's Play". Andy invites the entire office to his community theater production of "Sweeney Todd" in hopes that Erin will attend. Michael tries to put his jealousy aside and enjoy the performance while Jim and Pam struggle with their incompetent babysitter.