Web mining is used to extract knowledge from web data. Mainly there are three categories of web mining which are Web Content Mining, Web Structure Mining and Web Usage Mining. Web content mining sometimes referred to as text mining is used for scanning and mining the text, pictures and graphs of a Web page. Structure mining links the web pages using keyword association etc. and it overcomes two main the problems of web search i.e. irrelevant search results and inability to index related information provided on the Web. It makes the navigation easier by providing hyperlinks between linked sites. Web Usage Mining discovers interesting usage patterns from web usage data and provides the paths leading to accessed Web pages. This information is often gathered automatically by capturing the access logs of users visiting the website. It provides valuable uses to businesses marketing. Business can use web mining to improve marketing.