Grenades are one of the most important things to stay alive. You can make the enemy defense fly away and make them dizzy with concussion grenades and you can kill or damage your enemy very hard with a normal grenade in a heavy combat. The grenades in TFC remain mostly unchanged from their move to HalfLife, but a few things should be noted.

Firstly, the concussion grenade's effect does not last as long as it used to; if you are near the center of the blast of your own grenade, it lasts a mere 6 seconds or so for the medic. With other classes it will last longer. If you want to be one of the top medics, you'll have to learn concussion jumps. This isn't easy to learn and you will have to practise it very much, but it's a lifesaver. With concussion jumps you can easily pass a heavy defense, because they're not expecting you from the air or the place you jumped to.

Secondly, the standard hand grenades are more powerful than in the original TF, so take care when using them as you could seriously decrease your health if you come in range of the blast. People who (have) play(ed) Quake TF probably know the grenadejump(Just hold your grenade and walk against a wall, the blast will shoot you up). When you try this in TFC against a wall, you will notice you wont fly up... You probably will just fly sideways. That's why you need a corner to grenadejump in TFC. Stand in the corner and hold the grenade.

The best buttons to put grenades on are your right mouse button and INS or CTRL cause there you can use them easily (I see much people with their grenades on some letter button and that way you cant use them in heavy combat). Also a very important thing with grenades is timing. I will put a grenade timer here as soon as I know how :).