Recently, Lucasfilm has announced that all of the Expanded Universe (EU) content is now considered Non-Canon. For those who aren't aware what Canon and Non-Canon is, Canon is when books, videogames, or movies actually happened in the series timeline. Non-Canon is when something never actually happened in that series, which can result in a different plot line. An example of this is the Star Wars: The Force Unleashed videogame series, which is indeed set in the Star Wars Universe, but is a different plot line, and never actually happened in the main story line (movies). Before Lucasfilm announced it, all Expanded Universe material was considered Canon. The reason they changed this is because Lucasfilm wanted to create a new story. This way, people wouldn't already know what to expect in the Sequel Trilogy, which is set in the same time as the Expanded Universe (after Episode 6).
According to Wikipedia: "The official Star Wars canon consists of the seven released Star Wars theatrical feature films, the Star Wars animated film and television series The Clone Wars and Star Wars Rebels, and any other material released after April 25, 2014, unless otherwise stated"(Wikipedia).
If you want to know more about what is Non-Canon and what is Canon, check out either Wikipedia, or Wookieepedia, The Star Wars Wiki.
"Star Wars Canon." Wikipedia. Wikimedia Foundation. Web. 23 Dec. 2015.