Sometimes you want to identify a SPAM message source or just to find out who left that blog comment you might want to know to whom the IP block has been assigned. Though it is difficult to pinpoint it to an individual organization (especially SMEs who will have only few IP numbers or Dial-up/Home users where the IPs will be in their ISP’s names) there is a service that can give you some information. You can American Registry for Internet Numbers Whois Service or Asia-Pacific NIC’s Whois Service. Use one of the services and input the IP address for which you are interested to find the block owner.