It depends where it is Dirk
(there was a thread on this a few months or so ago with lots of comments, but I'll give you a few pointers).
I get chafing on my inner thighs from them rubbing together. It started when I put on muscle a few years ago (seems alot of people get this...in the Australian Army, they issue bike shorts as standard). Same would happen if you are carrying unwanted flab. Best solution for me here is to wear lycra/spandex bike shorts (without chamois padding-there are lots of running specific versions these days-in fact im aiming to buy a new pair tomorrow). Gels, etc as already mentioned also help, though I don't ever need both at the same time.
I've had a bit from wearing briefs in other places, usually on my but cheeks or bottom of lower back from seems/elastic and pack rubbing. This is usually from jocks I'm not used to and that are cotton with thicker elastics. Going commando under the bike shorts fixes this, and if I do this I normally wear shorts with mesh liners to give me support. I'm hoping my next pair of lycra shorts have better support.
One of my mates gets shocking chafing in places where u really dont want it, like right up top in between his legs, scrotumm (bad spelling is so that it passes the profanity filter...sorry BPL, but I'm being serious here not offensive), etc. We haven't solved it, but the gels, hydropel (the main one we use), etc, help, as does airing/reducing sweating. Cleaning would help, but it still happens when he's clean. Sometimes he just has to slow down so he doesn't sweat as much. I reckon he should clean shave regularly (like daily) down there, but thats a real hassle.
Hope this helps.