Beat the following modes in order - "Training", "Time Trial", "Gun Shooting", "Survival." Note: Completing each mode will unlock the next mode in the sequence. "Technical demonstration" mode will now be unlocked. Use it to watch the CPU demonstrate its best time with the gun.

When you beat the game, if you leave with Otacon, he will give you a prototype of an item called "Stealth." This allows you to walk near, through, and around guards, through trip lasers, and in the field of vision of cameras without alerting. This appears in your inventory when you start your second game.

First you have to get some C-4. Now sneak up behind a soldier and place it on his back. Try not to get to close or he may notice you and shoot you. This is is easier to do if you have the stealth suit. When you do get it on him, he will continue on his regular route. Find a good hiding place that is a safe distance from your intended victim, and press O to detonate.

When you beat the game, if you leave with Meryl, she will give you a prototype of an item called "Bandana." This gives you infinite bullets with any weapons you have. This appears in your inventory when you start your second game.

Beat the game twice and get both endings (one with Meryl and one without). When you play a third time, enter the elevator in the Cargo Dock. You'll remove your scuba gear and change into a tuxedo.

Beat the game twice and get both endings (one with Meryl and one without). When you play a third time, the ninja will be wearing a cool red and black outfit.

Beat the game and get the bandana. When you get the Fa-Mas, shoot all of your bullets except the last 2. Now put on the bandana and you will fire all tracers. You can now aim accurately with the Fa-Mas.

This is a cheat for those who feel they need to see the most ever bared on the Playstation. On the level where you try to save the Darpa chief in the cell, you will meet Meryl, who helps you shoot the intruders after the chief dies. You kill the gunmen and after the cinema sequence go back into the cell where you saw a man naked on the floor. Now get on the ground and take out your scope. You'll notice that the guy's butt is censored, but when you scope in ALL THE WAY you'll notice something the company never thought about.

Every second time you play, the initial cut scene when Solid Snake emerges from the water is shown from a different angle. This alternate start is repeated back and forth with the original cut scene from the beginning onward.

When fighting hand to hand with Liquid at the end, hit the Circle button on the second controller and it shows the stats of the fight.

When he uses his stealth put on the Thermal Goggles. This way when he uses his stealth you will be able to see where he goes.

Some of Mantis' reactions depend on the save games of other Konami games you have on your memory card. Try confronting him with a Castlevania, ISS Soccer, Suikoden or Silent Hill save game on your memory card for startling revelations.

After Mantis reads your mind, the screen will go black for a second before the battle begins. To make the fight MUCH easier, simply plug the controller into the "controller two" slot. He won't be able to read your mind anymore and will be easier to kill.

While fighting Mantis, push the first person view button (Triangle). Now you are looking through Mantis' eyes instead of Snake's. This is a useful way to find Mantis while he's invisible.