I will be lecturing on group theory next semester, for the first time in a long while.
This is a Masters level course, so has to assume quite a bit of background knowledge from earlier courses. I expect that many of the students taking the course will either have forgotten this material, or never learned it in the first place.
So I have produced a set of revision notes, and put them on the web, at http://www.maths.qmul.ac.uk/~pjc/MTHM024/gtrev.pdf. The course is about finite groups, and I have compressed the background into 30 pages (largely by leaving out proofs). This is more than I want to post here, so please use the link instead.
Feel free to use the notes yourself, and please send me corrections!