Web analytics is the measurement and analysis of internet data to understand and optimize website usage. It provides information on traffic, page views, and popularity trends which is useful for market research and assessing advertising campaigns. Web analytics tools can measure return on investment, identify top referral sources, optimize conversions, and save on customer support costs. Popular free and paid tools include Google Analytics, Compete, Quantcast, StatCounter, WebTrends, ClickTale, and Crazyegg which provide metrics on traffic, user behavior, and usability.