If you look up 'sum' in the dictionary - and I did - you'll see that the first meaning given is "an amount of money", so we might say that a million pounds is a very large sum, or that it is a substantial amount of money. A sum of money and an amount of money are effectively the same thing. They're also grammatically similar - they're both countable nouns and have plurals: 'sums' and 'amounts'. But both words have other meanings too. A sum is a calculation, for instance... "I was never any good at sums at school", I might say. 'Sum' can also mean 'total' - there was a film recently called "The Sum of all Fears". We can also use 'the sum' to suggest that all of something is not sufficient, for example: "If that's the sum of your ideas, I'm sorry I asked." This means that the person is not happy with the ideas that they've been given. And we frequently use the collocation 'a lump sum' to mean money that you give or receive all at once rather than in several different payments. For example: "Instead of paying back her bank loan each month, she managed to pay it all in a lump sum." I'd say that 'amount' is probably used more often than 'sum' - we use it frequently to talk about how much of something there is, or possibly to emphasize the degree or extent of something abstract. "You'll need to do a fair amount of work to finish on time", for example. We can also use it as a verb - "to amount to something". It describes the relative importance of something, for example: "I don't know if the rumours will amount to anything, but there is a lot of interest in the story." The last thing to say is that we should be careful using 'amount' with countable nouns - an amount of people, or cars for example. It's actually quite common to hear native speakers say this, but they should be saying: "A number of people" "A number of cars" - and some people get quite angry about this mistake. Quite a number of people, in fact! Thanks for your question Teresa.