There are many mods available, and Colossal Order cannot be expected to ensure that they will all still work after a patch, though they often work with modders to help them know what is coming. Often when game patches are released, information on mod incompatibilities gets posted on the Cities Skylines Paradox forum by helpful fans. Many mods will be updated by their creator or others, while some may no longer be supported.
Mods make changes to or add to the game code, and when the game is updated ( patched), some mods may stop working properly. Mods are executable code, and as such there is always some risk in running code that you do not know the contents of. There are many mods in the Steam Workshop that can be amazing to use, and this section is not meant to discourage their use, but there are some downsides which you should be aware of.
In the game's main menu, they are found in the Content Manager in the MODS section, where they may be turned on or off. There are a few 'built-in' mods that come with the game.
