Search engines are the hub for information retrieval from the web. But due to the web spam, we may not get the desired information from the search engines. The phrase web spam is used for the web pages that are designed to spam the web search results by using some unacceptable tactics. Web spam pages use different techniques to achieve undeserved ranking in the web. Over the last decades researchers are trying to design different techniques to identify the web spam pages so that it does not deteriorate the quality of the search results. In this paper we present a survey on different web spam techniques with underlying principles and algorithms. We have surveyed all the major spam detection techniques and provided a brief discussion on the pros and cons of all the existing techniques. Finally, we summarized the various observations and underlying principles that are applied for spam detection techniques. Keywords:TrustRank, Anti-TrustRank, Good-Bad Rank, Spam Detection, Demotion