system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What, or Who determines whether the Dollar/Euro/GBP etc rises or falls in value?

I see in the news everyday the fluctuating value of the USD, especially againt the Australian Dollar now, and I am wondering who or what determines this?

Edit - Thanks for all the responses! Really quite helpful =)
gpt
The demand for those currencies.  If people buy more Australian products, or more iPods (or let's be real, Treasury Bonds,) or more German cars, then they need the currencies of those countries to make their purchases.  The increase in demand for a currency increases that currency's value.