I realised that when I wrote the ISNA function article that I had never written an explanation of VLOOKUP. I want to write up explanations for a umber of other functions in the future like COLUMN, ROW, MATCH and INDEX followed by OFFSET. All these make lots of sense when you use them with the VLOOKUP function. So I though it best to start with this function. I will also say that everything I write about VLOOKUP here applies to HLOOKUP as well. the only difference is the orientation, that is VLOOKUP looks across columns from left to right, and HLOOKUP looks down rows from top to bottom.
The built in Excel Help is very good at helping with this function. However it doesn't point out many of the pitfalls than occur in common use.