It sometimes seems as though every day another bank or building society needs to be shored up as fast as possible - or else life as we know it will come tumbling down. And as the emergency scaffolding becomes ever more byzantine, so the whole thing becomes ever more baffling to those of us who didn't do economics at school, and had to have our mortgages explained to us very slowly, in words of one syllable.

What we do understand - or, more realistically perhaps, often don't quite understand but are gobsmacked by - is the size of the numbers involved. £500bn rescue packages. £37bn bailouts. Responsibility for £260bn-worth of risky assets. £75bn in quantitative easing. £20bn stimulus packages. (Not to mention President Obama's nice round trillion-dollar rescue plan.)

That, regardless of your levels of comprehension, sounds like a lot of money. Where is it coming from? Surely our taxes can't be paying for all of it? Where is it going? Will we ever see any of it again? What do all those words mean? I called economists, I called thinktanks. I contacted the Bank of England. Some were very patient, others condescending. The Financial Services Authority simply referred me to the Treasury. Nearly everyone, in fact, eventually pointed me to the Treasury. The Treasury sounded tired.

In the end, I began at the very beginning. The nature of money seemed a very good place to start. Money is all about trust. Even cash is only a promise. Look at a £10 note: "I promise to pay the bearer on demand the sum of ten pounds." As the economic historian Niall Ferguson puts it in his most recent book, The Ascent of Money, "Money is a matter of belief, even faith: belief in the person paying us; belief in the person issuing the money he uses or the institution that honours his cheques or transfers. Money is not metal. It is trust inscribed. And it does not seem to matter much where it is inscribed: on silver, on clay, on paper, on a liquid crystal display. Anything can serve as money, from the cowrie shells of the Maldives to the huge stone discs used one the Pacific islands of Yap. And now, it seems, in this electronic age, nothing can serve as money too."