It will checks where the page is visiting the first time or not If (!ispostback==true) then page is visiting at first time if (!ispostback==false) then u are second time or more number of times visited Advantages:Instead of loading same date to control you are already loaded that data. so u just check where first time or second time. when will use1) if you what to bind data to Grid view or drop down list or etc.only once when the page load it will use full.2) to store session values to variables