At the main menu, select "Options", then choose the "Keyboard/Mouse" selection. Enable the "Allow Developers Console" option.
While playing the game, press ~ to display the console window. Enter "sv_cheats 1" to enable cheat mode.
Then, type one of the following codes and press [Enter] to activate the corresponding cheat function:

Result --- Cheat Code

Invincibility --- god

Player can take damage but cannot die --- buddha

No clipping mode --- noclip

Toggle placing portals anywhere --- sv_portal_placement_never_fail [0 or 1]

Spawn Companion Cube --- ent_create_portal_companion_cube

Spawn dune buggy --- ch_createjeep

Spawn reflector cube for lasers --- ent_create_portal_reflector_cube

Turrets will not shoot at you --- notarget

Set game speed; default is 1 --- host_timescale [0.1 through 2]

Set gravity; default is 600 --- sv_gravity [number]

First person view --- firstperson

Third person view --- thirdperson

Shoot Conversion Gel out of your face --- ent_create_paint_bomb_portal

Shoot Propulsion Gel out of your face --- ent_create_paint_bomb_speed

Shoot Repulsion Gel out of your face --- ent_create_paint_bomb_jump

Shoots water out of your face --- ent_create_paint_bomb_erase

Set minimum speed in seconds Portal Gun shoots when click is held; default is "0.5" --- portalgun_held_button_fire_fire_delay [number]

Set minimum speed in seconds Portal Gun is fired; default is "0.20" --- portalgun_fire_delay [number]

Set acceleration of the speed gel; default is "500.0f" --- sv_speed_paint_acceleration [number]f

Set maximum speed obtainable from speed gel; default is "800.0f" --- sv_speed_paint_max [number]f

View frame rate --- cl_showfps 1

View your position and speed cl_showpos 1
Toggle cheat mode --- sv_cheats [0 or 1]