The capabilities and rapid progress of web Geographic Information Systems (GIS) are directly tied to Internet and web history and functionality, so understanding the basics of the web is necessary to appreciate how many web GIS techniques actually work. This chapter discusses popular web GIS applications and techniques, as well as more niche web GIS of special interest to some GIS practitioners. Many web GIS applications are aimed primarily at GIS users and website designers, as well as data analysts and other map producers, rather than the general public. One of the innovations that web GIS has brought to the table is the capability to run GIS operations completely within an Internet browser to create and manipulate maps. However, even with the advances that have been made in web GIS, desktop GIS software typically still has more advanced capabilities than online web mapping platforms.