Uncharted Waters Online, referred to as Great Voyage Online in Japan (Daiko-kai Jidai Online), is a MMORPG developed by KOEI based on the Rekoeition Uncharted Waters series of games. Set in the Age of Exploration players act as adventurers, soldiers, or traders, and engage in combat, exploration, and trade within the game.

Uncharted Waters Online is currently only available on the Windows platform in Japanese, Korean, traditional Chinese, and simplified Chinese, and will be made available on the PlayStation 3 in 2009.[1] Koei Co. has only made reference to an eventual Western release mentioning "the development of the major Asian markets, each in turn throughout the continent, and will take the route towards the European and North American market"

The U.S. branch of Koei has only mentioned that a North American release is "To Be Determined" as part of their 2006 E3 announcement. Contrarily, KOEI makes no mention of a Western release in their 1st quarter plan for 2007 only highlighting the simplified Chinese release . Criticism amongst western fans against Koei is concerned that all of Koei`s MMORPGs will remain Asia-only. Although since the PS3 is not region locked there is the opportunity for buyers to export.

Uncharted Waters Online is set within several timelines during the Age of Exploration as a romantic and historic fictional account of the era. Inconsistencies are found in the presence of Christopher Columbus and Elizabeth I of England as well as in some quests. However despite some of these timeline inaccuracies the game offers educational content in the form of exploration. Players can discover quests with historical value such as learning about Greek Fire or Seals. As an online game it offers Player vs Player combat areas and factional warfare as well as socialization in the form of in-game chat and card games.

Uncharted Waters Online features a variety of gameplay. The game can be divided into sea-based areas, land-based areas, and towns. Like most MMORPGs characters gain experience in skills and levels. The player may choose from among 6 nationalities: England, Netherlands, Ancien Régime in France, Spanish Empire, Kingdom of Portugal, Republic of Venice. As well the player may choose from several "occupations" after choosing a basic class: adventurer, merchant, and soldier. However players can learn and upgrade skills from other classes, albeit needing more experience points. Under certain conditions a player may change their class, occupation, and nationality. Players are able to trade, explore, battle and join in live events such as "Great Sea Fights".