IP geolocation aims at determining the geographic location of an Internet host, which can improve the performance and security of the Internet application, and bring about novel services. This paper firstly illustrates the concept and applications of the IP geolocation, and then categorizes current typical IP address geolocation algorithms into two classes, namly, client-independent geolocation algorithms and client-dependent geolocation algortithms. Next, the main ideas of the representative algorithms of each class are illustrated, and the privacy protection techniques and the influence of new techniques are discussed. Finally, a comprehensive comparison is made on the IP geolocation algorithms and systems, and the future trends of the IP geolocation are discussed.