With　the　emerging　microbloging　and　social　networking　platforms,　interests　become　more　and　more　important　for　user-driven　Web　applications.　Nevertheless,　there　is　no　specific　logical　system　that　can　be　directly　used　to　describe　human　interests　and　relevant　inference　rules.　In　this　paper,　we　introduce　the　interest　logic.　We　give　a　formal　language　to　describe　the　proposed　interest　logic,　then　we　discuss　its　semantics　and　axiomatization.　Following　the　proposed　interest　logic,　we　discuss　some　interesting　characteristics　of　human　interests.　With　the　discussion　of　factors　that　are　related　to　human　interests,　we　propose　some　possible　extensions　of　interests　logic.　Finally,　we　give　several　applications　of　interest　logic　on　the　Web　platforms　to　illustrate　its　potentials　and　effectiveness.