Dr. Horrible's Sing-Along Blog is a 2008 musical comedy-drama miniseries in three acts, produced exclusively for Internet distribution. Filmed and set in Los Angeles, the show tells the story of Dr. Horrible (played by Neil Patrick Harris), an aspiring supervillain; Captain Hammer (Nathan Fillion), his superheroic nemesis; and Penny (Felicia Day), a charity worker and their shared love interest.

The series was written by writer/director Joss Whedon, his brothers Zack Whedon (a television writer) and Jed Whedon (a composer), and writer/actress Maurissa Tancharoen. The team wrote the musical during the 2007–2008 Writers Guild of America strike. The idea was to create something small and inexpensive, yet professionally done, in a way that would circumvent the issues that were being protested during the strike. Reception has been overwhelmingly positive. On October 31, 2008, Time magazine named it #15 in Time's Top 50 Inventions of 2008. It also won the People's Choice Award for "Favorite Online Sensation", and the 2009 Hugo Award for Best Dramatic Presentation, Short Form. In the inaugural 2009 Streamy Awards for web television, Dr. Horrible won seven awards: Audience Choice Award for Best Web Series, Best Directing for a Comedy Web Series, Best Writing for a Comedy Web Series, Best Male Actor in a Comedy Web Series (Harris), Best Editing, Best Cinematography, and Best Original Music. It also won a 2009 Creative Arts Emmy Award for Outstanding Special Class – Short-format Live-Action Entertainment Programs.