The Internet evolved by end of the 80s from an US research network and transformed into a world-wide network system of various communication and information services.
The Internet Protocol is a protocol group which forms the basis for the Internet. It has been developed on request of the US Department of Defense in the early 70s to allow the combination of multiple networks.
An Intranet provides a concept and structure similar to the Internet for a LAN. It therefore serves as a means for communication and information within enterprises, using the same services as in the Internet such as HTTP or E-Mail.