The best known system is the French Ancien Régime (Old Regime), a three-estate system used until the French Revolution (1789–1799). Monarchy was for the king and the queen and this system was made up of clergy (the First Estate), nobles (the Second Estate), and peasants and bourgeoisie (the Third Estate). In some regions, notably Scandinavia and Russia, burghers (the urban merchant class) and rural commoners were split into separate estates, creating a four-estate system with rural commoners ranking the lowest as the Fourth Estate. Furthermore, the non-landowning poor could be left outside the estates, leaving them without political rights. In England, a two-estate system evolved that combined nobility and bishops into one lordly estate with "commons" as the second estate. This system produced the two houses of parliament, the House of Commons and the House of Lords. In southern Germany, a three-estate system of nobility (princes and high clergy), ritters (knights), and burghers was used.
Today the terms three estates and estates of the realm may sometimes be re-interpreted to refer to the modern separation of powers in government into the legislature, administration, and the judiciary. Additionally the term fourth estate usually refers to forces outside the established power structure (evoking medieval three-estate systems), most commonly in reference to the independent press or media. Historically, in Northern and Eastern Europe, the Fourth Estate meant rural commoners.
During the Middle Ages, advancing to different social classes was uncommon and very difficult.
The medieval Church was an institution where social mobility was most likely up to a certain level (generally to that of vicar general or abbot/abbess for commoners). Typically, only nobility were appointed to the highest church positions (bishops, archbishops, heads of religious orders, etc.), although low nobility could aspire to the highest church positions. Since clergy could not marry, such mobility was theoretically limited to one generation. Nepotism was common in this period.
Another possible way to rise in social position was due to exceptional military or commercial success. Such families were rare and their rise to nobility required royal patronage at some point. However, because noble lines went extinct naturally, some ennoblements were necessary.
"Medieval political speculation is imbued to the marrow with the idea of a structure of society based upon distinct orders," Johan Huizinga observes. The virtually synonymous terms estate and order designated a great variety of social realities, not at all limited to a class, Huizinga concluded applying to every social function, every trade, every recognisable grouping.
There are, first of all, the estates of the realm, but there are also the trades, the state of matrimony and that of virginity, the state of sin. At court there are the 'four estates of the body and mouth': bread-masters, cup-bearers, carvers, and cooks. In the Church there are sacerdotal orders and monastic orders. Finally there are the different orders of chivalry.