The expansion of online gaming has reflected the overall expansion of computer networks from small local networks to the Internet and the growth of Internet access itself. Online games can range from simple text based games to games incorporating complex graphics and virtual worlds populated by many players simultaneously. Many online games have associated online communities, making online games a form of social activity beyond single player games.

The rising popularity of Flash and Java led to an Internet revolution where websites could utilize streaming video, audio, and a whole new set of user interactivity. When Microsoft began packaging Flash as a pre-installed component of IE, the Internet began to shift from a data/information spectrum to also offer on-demand entertainment. This revolution paved the way for sites to offer games to web surfers. Most online games like World Of Warcraft, Final Fantasy XI and Lineage II charge a monthly fee to subscribe to their services, while games such as Guild Wars offer an alternative no monthly fee scheme. Many other sites relied on advertising revenues from on-site sponsors, while others, like RuneScape, let people play for free while leaving the players the option of paying, unlocking new content for the members.

After the dot-com bubble burst in 2001, many sites solely relying on advertising revenue dollars faced extreme adversity. Despite the decreasing profitability of online gaming websites, some sites have survived the fluctuating ad market by offsetting the advertising revenue loss by using the content as a cross-promotion tool for driving web visitors to other websites that the company owns.
Flash games are electronic games that are played online via the Internet through browsers such as Internet Explorer, Mozilla Firefox, Safari, Opera, Lynx. They are distinct from normal video and computer games in that they do not require any client side software to be installed. There are games that rely solely on client-side technologies such as a web browser and a common plugin such as Java or Flash or built in technologies like Ajax and the canvas object, whereas other also employ server-side scripting. The latter case are typically (massive) multiplayer games, whereas the client-side games are typically single-player games. A game played in a browser is often called a browser-based game.