I'm no historian, but certainly someone who's interested in it, and Medieval Europe especially isn't something I know too much about, outside of the usual common knowledge - But I was just wondering - In a Feudal Society, with most of the population being Serfs who never really left their villages, before the idea of a middle class - Who did the trading?
I mean, who took goods to other countries and sold in markets? Was it just a few lucky Serfs who managed to escape the classist mould?
Incidentally, I'm probably being an idiot, so sorry for that in advance.
Trade in the Medieval era was very important around the Mediterranean sea. The Iberian and Italian peninsula both benefited greatly from trade and it helped to launch kingdoms in those nations into powerful states. During the Medieval era, trade with the Middle East was highly valued due to their access to spices and exotic goods. The Big Four of the North/Central Italian peninsula (Florence, Venice, Genoa and Milan) controlled a large amount of the trade that flowed into Northern Europe. Merchants or trading guilds, would finance expeditions to various parts around the Mediterranean and then send out merchants (either by land or sea) to other parts of Europe to sell and collect higher profit. Some trips could return enough to finance a series of other expeditions.
Most cities had families that tended to have enough financial power to sponsor such ventures. In The Republic of Venice for example, we have records of a Mocenigo family. An important family that established its reputation by financing trips to collect spices (most valuable spices being pepper and ginger) and exotic goods. Often such families would go into rivalries, one of the most famous rivalries is the one established in the city of Florence which ultimately led to the rise of the Medici family. The rivalries most of the times led to bloodshed (in the case of the Medici, the bloodshed was quite big.) The Medici made their fortune from the trade of textiles, originally within the Italian peninsula, eventually with powerful nations such as France and Spain. However, not all families grew to the power of the Mocenigo and Medici, sometimes families went bankrupt. Traveling for trade was dangerous. The seas were rough, pirates were everywhere, military fleets often raided, etc. Families, if they took out loans, would go bankrupt if a trip failed. A trip could make or break a family. With this came the development of trade contracts, these were particularly popular with Florentine and Genoese merchants. These were notarized documents and they provided the merchant investors with a safety net should something go wrong.
Overall, the Italian City States would establish their financial dominance in Medieval Europe mostly through trade. The Venetians and Genoese would go on to be respected throughout the world as some of the best sea captains and sailors. The grasp of the Italian dominance over trade in the Mediterranean would only be broken centuries later by the Spanish and Portuguese. Ironically, some of the earlier expeditions of those countries, were partly financed in the hope of crushing the dominance of the already established powers in the region.
There is a LOT of material available regarding this topic. I am sure some of the other Medievalists will have plenty to add, specially with Northern European trade.
I recommend the following books:
*The Economy of Renaissance Florence by Richard A. Goldthwaite. An excellent text with a ton of detail regarding how trade worked in Florence at the time: prices, items, contract explanations, etc. Highly recommended.
*Trade and Traders in Muslim Spain: The Commercial Realignment of the Iberian Peninsula, 900-1500 by Olivia Remie Constable. Great text for understanding cross-cultural trade between Christians and Muslims during the Middle Ages. its benefits and consequences. Also highly recommended.
*Commercial Agreements and Social Dynamics in Medieval Genoa by Quentin van Doosselaere. Just like Goldthwaite's book, Van Doosselaere does the same but with Genoa. Very thorough explanation and analysis of the rise of commerce in Genoa and its affect in Genoese society.
Finally, a large number of documents in regards to England are part of the Venetian archive. They are available online for free and have very interesting details about trade prices and ship arrivals. Primary sources.