Since I like the relatively short writeup in where does the money come from?
, here's a new node to discuss some other issues in macroeconomics
alex_tan is right; I was talking more about wealth than money itself. Until recently, money was based on the value of gold. Originally, the only reason a gold coin was more valuable than a lump of gold is that an authority was willing to validate its weight and purity. Until the 20th century, paper money was literally exchangeable for gold and was valueless if that exchange couldn't be made--the 18th and 19th centuries are filled with economic crises that occured when organizations (not always governments) issued paper money that they couldn't cover with gold, which meant that people who held the paper were wiped out when the gold ran out.
In the 20th century most nations went off the gold standard, so money is now nothing more than a social construct. This is why the relative values of different currencies change over time--the money issued by a particular nation has no value except what people are collectively willing to give it.
The origin of wealth opens up another range of problems. One of the ongoing problems in capitalist economies is that the people who contribute the most labor don't get the most benefit. The US government has, for many years, been engaged in making sure that all new wealth stays out of the hands of people who actually work--and, within the capitalist economic system, that decision makes sense. Karl Marx saw this problem and said that the solution was to make workers the owners of the companies that employ them, so that there's no longer a division between employers and employed. This has been tried with some success, and in fact the creation of the mutual fund and the 401(k) have moved the United States in a Marxist direction...sort of.
It's true that mutual fund ownership doesn't give workers control over their companies--but it does give them a share (albeit a small one) in economic growth. I was able to put away $500 in a 401(k) a couple years ago...after employer matching and interest, it will pay for a full year of my retirement later on, thanks to the leaps that the stock market. While it's not really what Marx had in mind, it is at least a step in the right direction.