The Knowledge Graph is a knowledge base used by Google to enhance its search engine's search results with semantic-search information gathered from a wide variety of sources. Knowledge Graph display was added to Google's search engine in 2012, starting in the United States, having been announced on May 16, 2012. It provides structured and detailed information about the topic in addition to a list of links to other sites. The goal is that users would be able to use this information to resolve their query without having to navigate to other sites and assemble the information themselves. The short summary provided in the knowledge graph is often used as a spoken answer in Google Now searches.
According to Google, the information in the Knowledge Graph is derived from many sources, including the CIA World Factbook, Freebase, and Wikipedia. The feature is similar in intent to answer engines such as Ask Jeeves and Wolfram Alpha and efforts such as Linked Data and DBpedia.
As of 2012[update], its semantic network contained over 570 million objects and more than 18 billion facts about and relationships between different objects that are used to understand the meaning of the keywords entered for the search. 
In August of 2014, Google announced a new initiative, the Knowledge Vault, which derives much of its data from the Knowledge Graph and the sources thereof, as well as harvesting its own data, ranking its reliability and compiling all results into a database of over 1.6 billion facts collected by machine learning algorithms.
In November 2014, Google began displaying social profile icons for certain brands, companies and musicians in their respective Knowledge Graph results. The social icons linked to their social network profiles which included Facebook, Twitter, Google +, YouTube, Instagram, Myspace and LinkedIn. Months after, Google released guidelines for how to enable this feature if you would like to have your social profiles displayed in the Knowledge Graph.
We have had internal debates about when to ship something. We could come out with something now like them, but it wouldn't be state of the art. It's too constrained to be an agent now. We are not shipping until we have something more revolutionary than evolutionary.
During the Google I/O conference in May 2013, Google's Amit Singhal presented on the future of search, explaining that a search engine's three primary functions will need to evolve and that search will need to: 1. Answer, 2. Converse, and 3. Anticipate. As part of his keynote talk, Singhal stated, "A computer you can talk to? And it will answer everything you ask it?"
- Singhal, Amit (May 16, 2012). "Introducing the Knowledge Graph: Things, Not Strings". Official Blog (of Google). Retrieved May 18, 2012.
- (registration required) Waters, Richard (May 16, 2012). "Google To Unveil Search Results Overhaul". Financial Times. Retrieved May 16, 2012.
- Bohn, Dieter. "Google Now: behind the predictive future of search". The Verge. Vox Media, Inc. Retrieved 23 March 2015.
- Staff (December 4, 2012). "Get smarter answers from the Knowledge Graph from Português to 日本語 to русский". Google. Retrieved December 4, 2012.
- Akesson, Andrew (August 27, 2014). "Google My Business Profiles Start Ranking In Non-Branded Searches". Retrieved September 9, 2014.
- Newton, Casey (December 14, 2012). "How Google is taking the Knowledge Graph global". CNET.
- Brown, Aaron (December 12, 2012). "Get smarter answers from the Knowledge Graph from Português to 日本語 to русский". Inside Search (Google).
- Orlowski, Andrew (13 January 2014). "Google stabs Wikipedia in the front". The Register. Retrieved 15 January 2014.
- Kohs, Gregory (6 January 2014). "Google’s Knowledge Graph Boxes: killing Wikipedia?". Wikipediocracy. Retrieved 15 January 2014.
- Marshall, Gary. "Like Harvey Dent, Google has become Two Face". TechRadar. Retrieved 15 January 2014.
- Andrieu, Olivier (14 January 2014). "Le Knowledge Graph de Google ferait baisser le trafic de Wikipedia" (in French). Abondance. Retrieved 15 January 2014.
- "Google’s Knowledge Graph Finally Shows Social Networks Not Named Google+". Search Engine Land.
- "Specify your social profiles to Google". Google Developers.
- "Transferring Data to Wikidata and Shutting Down". Google+. Dec 16, 2014. Retrieved Dec 18, 2014.
- Dan Farber (30 July 2013). "Microsoft's Bing seeks enlightenment with Satori". Cnet. CBS Interactive Inc. Retrieved 3 December 2013.
- Google (May 15, 2013). "Google I/O 2013: Keynote".
- Jessica Lee (16 May 2013). "OK Google: 'The End of Search as We Know It'". Search Engine Watch. Incisive Interactive Marketing LLC. Retrieved 20 May 2013.