From the longer Wikipedia page 
The Company of Merchant Adventurers of London brought together London's leading overseas merchants in a regulated company, in the nature of a guild. Its members' main business was the export of cloth, especially white (undyed) broadcloth. This enabled them to import a large range of foreign goods.
The company received its royal charter from King Henry IV in 1407, but its roots may go back to the Fraternity of St. Thomas of Canterbury. It claimed to have liberties existing as early as 1216. The Duke of Brabant granted privileges and in return promised no fees to trading merchants. The company was chiefly chartered to the English merchants at Antwerp in 1305. This body may have included the Staplers, who exported raw wool, as well as the Merchant Adventurers. Henry IV's charter was in favor of the English merchants dwelling in Holland, Zeeland, Brabant, and Flanders. Other groups of merchants traded to different parts of northern Europe, including merchants dwelling in Prussia, Sconce, Sound, and the Hanse (whose election of a governor was approved by Richard II of England in 1391), and the English Merchants in Norway, Sweden and Denmark (who received a charter in 1408).
Under Henry VII's charter of 1505, the company had a governor and 24 assistants. The members were trading capitalists. They were probably mostly composed of London mercers. The company also had members from York, Norwich, Exeter, Ipswich, Newcastle, Hull, and other places. The merchant adventurers of these towns were separate but affiliate bodies. The Society of Merchant Venturers of Bristol were a separate body, chartered by Edward VI in 1552.
Under Henry VII, the non-London merchants complained about restraint of trade. They had once traded freely with Spain, Portugal, France, Italy, and the Netherlands, but the London company was imposing a fine of £20, and drove them out of their markets. Henry VII required the fine to be reduced to 10 marks (£3.6.8 —- £1 = 3 English marks; 1 mark = 6s 8d). Conflict arose with the Merchants of the Staple, who sought to expand from exporting wool through Calais to exporting cloth to Flanders without having to become freemen of the Merchant Adventurers. The Merchant Adventurers kept control of their trade and Flanders as their port. Foreign merchants of the Hanseatic League had considerable privileges in England trade and competed with the Merchant Adventurers. These privileges were revoked by the English government in the mid-16th century.