HONOLULU -- Stolen art is big business. According to Interpol, the traffic in stolen art is worth about $5 billion a year, about as much as the illegal trade in arms and drugs. Accurate estimates of the trade are hard to come by, but this figure is almost certainly low. After all, how does one value one-of-a-kind historical and cultural objects? In those cases, price tags are meaningless. The uniqueness of these objects makes them even more treasured by collectors. Typically, the only constraint they face is the size of their bank account and their readiness to pay.

This month, the rules will change for Japanese collectors. On Dec. 9, the Convention on the Prevention of the Illicit Import, Export and Transfer of Ownership of Cultural Property goes into effect in Japan. The convention, adopted by UNESCO's General Conference in November 1970, is the first global legal instrument that protects cultural property against pillage and illegal sales. Although Japan will be the 95th country to ratify the convention, signing on is a big deal. First, Japan is one of the world's wealthiest countries and the home of many collectors. It is a critical node in the international art network. Second, Japan has an enormous amount of stolen art and cultural artifacts.

Much of the damage was done during Japan's imperial period, when colonial administrators looted the lands they controlled. According to the Cultural Properties Administration of Korea, there are at least 34,157 cultural objects of Korean origin in Japan -- and those are only the objects that are known to be there. When objects that are thought to have been stolen are included, the number more than doubles to 75,266 objects. According to another estimate, Japanese colonial officials and private collectors took at least 100,000 artifacts and cultural treasures from the end of the 19th century until Japan's defeat in 1945. There are more than 1,000 Korean artifacts at the Tokyo National Museum, more than 800 at the Osaka City Museum of Ceramics and more than 2,100 books in the Kyoto University Library.