The second screen refers to the use of a computing device (commonly a mobile device, such as a tablet or smartphone) to provide an enhanced viewing experience for content on another device, such as a television. In particular, the term commonly refers to the use of such devices to provide interactive features during "linear" content, such as a television program, served within a special app.
Social television creates a need and opportunity for interaction between the sender and content consumers. This involves new services, applications and changes in content production. The use of second screen provides a parallel path, whereby the user can become an active agent in the broadcast content or in just some other activity, rather than interrupt playback.
The concept is being expanded to include live events like keynote speeches, meetings and seminars where the "first screen" is the main presentation screen, and participants use smartphones and tablets to mirror the main screen and/or view ancillary information.
Several studies show a clear tendency of the user to use a device while watching television. They also show a greater frequency of use of tablet or smartphone when watching television, and other studies distinguish a higher percentage of comments or posts on social networks, about the content that's being watched (Nielsen ratings)  As well, Google has published a study where they define some apparent new behaviors on the part of users when consuming content via multiple devices.
On these studies, many companies both in content production and advertising have adapted their formats to the user, trying to get maximum attention and thus profits. Applications are becoming a natural extension of television programming, both live and on demand.
Many applications in the "second screen" are designed to give another form of interactivity to the user and another way to sell advertising content. Some examples:
- Transmission of the Master's Golf Tournament, application for the iPhone (rating information and publicity) 
- TV programs broadcast live tweets and comment.
- Synchronization of audiovisual content via web advertising.
- Applications that extend the content information.
- Shows that add on their websites, content devoted exclusively to the second screen 
- Applications that synchronize the content being viewed to the portable device.
- Video game console playing with extra data, such as a map or strategy data, that synchronize with the content being viewed to the portable device.
- TV discovery application with recommendation, EPG (live content), personalization.
Projects and Research activity which is addressing 2nd screen includes:
- SAM: Socialising Around Media: Leading European Research Project on Second Screen, Content Syndication and Social Media.
Sports broadcasters, to stem the flight of the TV audience away from watching the main screen (new name for the television) to the second screen, are offering alternative content to the main program. The idea is to present content related to the main program, such as unseen moments, alternative information, soundtrack, and characters. Proposed new technologies allow the viewer to see different camera angles while watching the game.
TV2 (Denmark), Denmark's largest commercial TV channel, synchronized its Second Screen service to live events of the Giro d'Italia 2012 bicycling from May 5 to May 27, 2012, whereby viewers on all internet devices could get rider stats, biographies, news, stage reviews, city info, weather info and the like. Viewers scanned a QR code on the TV broadcast to get connected, or typed in a short URL.
In the US, HDNet Fights utilizes a second screen service to synchronize to live MMA broadcasts, where viewers on smartphones and tablets could get stats, vote on fights and rounds, chat, win prizes, and see how fellow second screen users voted to win fights.
- C-Cast, software which allows broadcasters to stream live content, such as clips or alternative angles, from their video servers to the audience's second screen.
- Smart TV.
- BskyB, an enhanced EPG to browse through programs after selecting some research criteria.
- at&t, a BskyB, an enhanced EPG to browse through programs after selecting some research criteria.
- at&t, a remote control main feature to launch the content from the second screen to the first screen through the set-top box.
- In the U.S., Tablets are TV Buddies while eReaders Make Great Bedfellows
- What Do TV-Social Media Multitaskers Talk About?
- The New Multiscreen World By Google - Understanding Cross-platform Consumer Behavior
- Changing the way we're watching TV
- The Masters Golf Tournament for iPhone 3GS, iPhone 4, iPhone 4S, iPhone 5, iPod touch (3rd generation), iPod touch (4th generation), iPod touch (5th generation) and iPad on th...
- Twitterrevolución | Edición impresa | EL PAÍS
- Tweeting for TV | Twitter Developers
- How It Works
- Umami for iPad - Your TV Companion on Vimeo
- X Factor UK for iPhone, iPod touch and iPad on the iTunes App Store
- MTV Video Music Awards | 2011 | Highlights, Winners, Performers and Photos from the 2011 MTV Video Music Awards | MTV.com
- http://news.cnet.com/8301-33692_3-57446945-305/e3-2012-year-of-the-second-screen-with-xbox-smart-glass-and-wii-u/ E3 2012: Year of the second screen with Xbox Smart Glass and Wii U
- http://techcrunch.com/2012/06/04/microsoft-introduces-second-screen-feature-xbox-smartglass/ Microsoft Introduces Second-Screen Feature, Xbox SmartGlass
- Sony announces PlayStation app for iOS and Android, will expand games to the second screen
- Sony Announces PlayStation 4, Second-Screen Experience PlayStation App for iOS
- Xbox SmartGlass official as second-screen feature
- SAM: Socialising Around Media
- Alternative angles in Sports broadcast
- Second Screen is future
- Giro 2.0 – second screen experiences
- Mobovivo Launches Social TV Platform to Utilize Second Screen - Techvibes.com
- Buckley, Sean. "Sony announces PlayStation app for iOS and Android, will expand games to the second screen". Engadet. Retrieved 5 May 2013.
- Lawler, Richard. "Xbox One SmartGlass brings more control, content to companion devices". Engadet. Retrieved 28 May 2013.
- 5 ways that the television industry uses Twitter.
- Yap TV.
- From television to the second screen.
- TV and social networking closer.
- Twitter CEO on Second Social Screen TV.
- TV with other electronic devices.
- Second Screen Networks.
- Social Yume Study.
- HDNet Fights Second Screen App.
|Primary Screen||Second Screen|
|Select Dish Network Receivers||iOS and Android devices using Dish Anywhere Mobile App|
|Select Disney Blu-Ray discs and DVDs||iPad and devices running Adobe Flash using Disney Second Screen|
|GameCube||Game Boy Advance using Nintendo GameCube–Game Boy Advance link cable|
|PlayStation 3||PlayStation Portable and PlayStation Vita using Remote Play|
|PlayStation 4||PlayStation Vita using Remote Play; iOS and Android devices using PlayStation Official App|
|Wii U||Wii U GamePad and Nintendo 3DS|
|Xbox 360||Windows 8, Windows Phone, iOS, and Android devices using Xbox SmartGlass|
|Xbox One||Windows 8, Windows Phone, iOS, and Android devices using Xbox SmartGlass|
|WWE RAW/ SmackDown/ Main Event||iOS, and Android devices using The WWE APP|