Fallout: New Vegas weapon mods

Overview
Several of New Vegas's weapons can be modified with mods.

There are multiple weapon mods for some weapons, and a maximum of three weapon mods can be attached to any one weapon. Once any weapon mod is attached it is permanent, so be wise in what you want to attach. For example, while an extended magazine is almost always beneficial, a scope has pros and cons. It may increase maximum range, but making it harder for close combat.

Mods are attached by having both the weapon and the mod in your inventory, then going to the weapons page on the Items tab within your PipBoy, highlighting the weapon you want to mod, and looking to the right of the info pane to see what button or key to use to open up the mod screen for that weapon. After you have selected a mod, the weapon name will have a + after it to show it has been improved. Modding a weapon also increases its value.

There are currently 11 vendors who offer weapon mods in the Mojave Desert:
 * Alexander, 188 Trading Post
 * Great Khan Armorer,
 * Blake, Crimson Caravan Camp
 * Vendortron, Gun Runners
 * Gloria Van Graff, Silver Rush, Freeside
 * Dale Barton, Fort Hill
 * Chet, Goodsprings
 * Michelle, 188 Trading Post
 * Knight Torres, Hidden Valley
 * Old Lady Gibson, Gibson Scrap Yard
 * Cliff Briscoe, Novac