i need to know the reference URL

Question

friends, i need to know the reference URL from which a person comes to my site. for example: i have a site named : www.abc.com if a person finds this link www.abc.com by searching on google.com then i want this information that the person is coming from google.com i have to maintain the reference URLs. i m working in ASP.NET i will apperciate if someone give me any idea to work on.