CS is an add on for Halflife that modifies the whole game. HL is single or multi-player. CS is just multi-player. In HL multi-player, you basicaly run like hell and just kill everyone and respawn when you die. In CS, you start off with $800 and have to buy weapons, ammo, and equipment. It's Terrorist against the counter terrorist with 2 basic scenerios(plant/defuse the bomb and Hostage rescue). Unlike HL, when you get killed, you don't respawn until the round is over. A round ends when, one of the teams gets all it's members killed, the bomb gets defused, or all the hostages are rescued. The more enemies you kill or rounds your team wins, the more money you earn to upgrade your weapons. Here is the kicker...if you get killed, you have to buy all your equipment again. When the map changes, everyone starts over and has $800 and a pistol. The game is very adictive and fun to play. If you get HL and dload CS, message NeoTechMan about his server. Alot of ppl here on Anandtech play there cause it's private and makes it more fun!