Why Is USD Sometimes First, Sometimes Second?

This might sound a bit weird, but I had a job interview, and one of the questions was this:

"In the currency pairs, why does USD sometimes come first (e.g. USDJPY), and sometimes it comes second (e.g. EURUSD)?"

This may well have been one of those questions that does not have a correct answer. It was one of those type of interviews.

Well, I think I found an answer, thanks to the magic of the Internet and the helpful people that reply to questions posted in forums.

I think this tradingmarkets.com page answers the question nicely:

In most cases, USD is the base currency, with the other currency in question being the quote currency. USD/JPY is an example.

There are a few exceptions, though. When it was introduced in 1999, the market authorities decided the Euro would always be the base currency in all traded pairs. Before that, the Pound (GBP) held that distinction. Thus, when traded against either of those, the USD is the quote currency (EUR/USD, GBP/USD). The same also holds for former British Commonwealth currencies the Australian Dollar (AUD/USD) and the New Zealand Dollar (NZD/USD).

So, Mr.Interviewer, if you happen to read this blog entry, there's your answer. Please give me the job :-)