The most common way is through the channels of De Beers: Diamond Trading Company (DTC).
The DTC is the rough diamond distribution arm of De Beers, and is the world's largest supplier of rough diamonds, by value.
The Diamond Trading Corporation's purpose is to stabilize prices when times are hard, and raise them with inflation and demand when times are good.
DTC holds ten week-long selling sessions called sight each year. These sights are by invitation only, and only a handful of diamond manufacturers from around the world (called Sightholders) are allowed to attend. The value of each sight varies from $500,000 to $2,000,000.
The « outside » market is the market « Outside DTC », i. e. not controled by De Beers.
There are other mining companies (BHP Billiton, Alrosa, Rio Tinto) operate diamond mines and sell their rough diamonds on the international market. These sales are like the sights of De Beers.
The major diamond manufacturing centers includes Israel, Belgium, India and New York. The most important is Antwerp in Belgium, more than half of the world market of polished diamonds passes by Antwerp.
In Belgium, approximately 1,500 diamond offices are located in Antwerp in a diamond district: Hoveniersstraat, Schupstraat, Rijfstraat and Pelikaanstraat.
The rough is distributed to the cutting centers and to dealers in Antwerp, where approximately 80-85% of the total rough diamond trade takes place.
The main diamond bourses are:
The conditions to become member of one of these bourses are very strict.