Link building is one of the SEO techniques to index a website on Google and other search engines. Often overlooked, this activity is extremely important to guarantee the credit of a web page. How does link building work? Google detect internal backlinks and backlinksfrom other websites, assigning a higher score on pages with many links, especially from websites considered authoritative in the same field. A backlink is considered as a reference: if an authoritative website put a link to my page, it means that my work has been positively evaluated. A backlink, to be most effective, must meet a precise syntax. First of all, it should not have the nofollow attribute that stops Google spiders. The words on which you insert the link must be related to the subject of my page and the same goes for the title of the link. In addition, it would be appropriate to include a link to a site that deals an argument similar to that of the destination page. Over the years it has grown to the importance of backlinks, but also the unfair activities that now are recognized through implementations of search engines like Google Penguin or Google Hummingbird that aim to provide the best user experience. How do link building in the right way? If we want to use link building to improve the Google ranking, we have to act in order to be linked by authoritative websites, blogs and forums remembering that only the links without nofollow tag are detected by Google. Links should be relevant and voluntarily granted by the author that believes that our contents are interesting. How not to do link building? If you don’t want to be considered a black hat by Google, with a consequent penalty, avoid unfair techniques. We shouldn’tlink our pages to link farms, sites that sell links and we shouldn’t build circuits that have the only purpose to link websites to each other. Sooner or later Google will find all the black hats. Get out of a penalty is a long and complicated process: it’s better to do a fair link building.