thin coating of grease on the core, you don't want to slop it on, just make sure you have enough that you won't have any air pockets. I like squirting a bit on then spreading it with a credit card. If anything, ere on a little to much, the heatsink will squeeze the excess out. If you're planning on overclocking, or have a really fast chip (above 1 ghz) you should really be sure to do a good job and have a VERY good heatsink.