Since the early 2000s, the art market has experienced a strong expansion both in volumes and in the prices of the art works sold. Nowadays, the art market is worth $50 billion worldwide, and the sales of certain artworks by artists such as Jean-Michel Basquiat or Jeff Koons are close to $100 million. Today, the number of private collectors in the world, which was estimated at 500,000 after the World War II, exceeds 120 millions.
In fact, the growth of the art market since the early 2000s is largely due to the skyrocketing rise of the museum economy, especially in China. Each year, about 700 new international museums open their doors to art lovers on all continents, of which more than two-thirds are located in China. However, to attract the public, each of these museums is ready to buy masterpieces in large quantities, even if it costs millions of dollars.
The volatility of the financial markets, the tendency to lower interest rates and political and fiscal uncertainties have prompted investors to turn to art works. This investment has become increasingly democratized thanks to digital technology: 98% of the 6,300 sales houses in the world is now present on the Internet, whereas they were only 3% in 2005. Since 20 years the art market has increased by more than 380% and its annual yield is between 10% and 15%.
Auction houses are private establishments whose role is to sell to the public art works belonging to private collectors. The auction market is characterized by a very high concentration of transactions, at least for the most important of them, between a small number of countries. It is mainly controlled by transnational companies, the two most important, Sotheby's and Christie's, form a quasi-duopoly. The origin of the two leading auction houses in the world is both very old and very local, since the company that later became Sotheby's was created in 1744, and Christie's in 1766, They're both from London.
As a result of their policy of expansion during the 1950s to 1970, Sotheby's and Christie's have become two structures of international scope. Since 1955, Sotheby's has opened an office in New York. Following the success of its American establishment, Sotheby's has opened offices in many countries in the late 1960s, including France, where it moved to Paris in 1967. It was in 1968 that Christie's moved to Paris, and opened a sales room in New York in 1977. Today, Christie's has 85 offices in 43 countries and 10 sales rooms. Sotheby's has a network of 11 sales rooms in 9 different countries, supplemented by 77 offices representation around the world.


The auctioneer is responsible for directing the auction between the people in the room, on the phone for private customers, offers from the internet relayed by of the assistants and the sealed offers filed before the opening of the session. The sale is accompanied by the edition of a catalogue where are presented the art works put on sale, as well as low and high estimates established by the experts of each artist.
The starting price of the auction is usually between 60% and 80% of the low estimate. The owner of a lot accompanies the sale of a reserve price below which the lot will not be sold (Passed). Otherwise the lot is awarded to the last bidder who offered the best offer and sale is concluded by a symbolic hammering of the auctioneer on his desk. The fees taken by the sales house lies between 20% and 30% of the hammer price. The number of unsold works during a session is around 15% and 35%.
The value of a piece of art is determined by taking into account many factors like its aesthetic and technical qualities, its dimensions, its history, the notoriety of the artist who created it, the context in which it is sold, etc. Large private collectors and investment funds who control the art market are pushing forward or, on the contrary, are making themselves felt by some artists, according to their own tastes or speculative strategies. The artist's rating fluctuates as a financial instrument. In addition, there is a lot of data on the art works and their authors, and their quotation is assessed on their sales history taking as a basis a period of several years. The estimation of a work is therefore based on both the supply and demand mechanism, and objective and subjective criteria.