Mods are enhancements to Warframe, Weapons, Companions, Arch-wings, Arch-Gun, Arch-Melee etc. There are more than 1100 Mods available. They can be purchased from Market, purchased from Baro, traded between players, and most importantly formed in various mission.

Extra Mods can be sold for credits or Endos. Early players find it easy to sell Mods to get some quick credits, but deeper in game, you will realize that getting Endos for the Mods will be a better options.

4 Mods can be fused to give a new random Mod. Modes can be upgraded with Endo and Credits.

Due to the shear high number of Mods, I am breaking up the list in the following groups. You can check the drop location and chances for Mods where available.

Warframe Mods

Weapon Mods

Companion Mods

Archwing Mods

Rivens

Railjack Mods