IMPORTANT
If you are upgrading from Beta 3 or earlier, you should verify back to an up-to-date vanilla install.
Beta 10 requires a new campaign.

Instructions
If you have ever played with any other mods on your EW install, or have changed some files yourself, verify back to a vanilla installation of EW before installing Long War. If you have any trouble with installation, do this as well.
Disable any antivirus software. We have specific reports that Comodo security software prevents a proper install, and BitDefender free crashes the game on startup.
Make sure you have the latest .NET Framework and Java installed.
Run the installer.
When you select your path to install the mod, you should receive a warning that the directory already exists. If you didn't, have you may have missed a step.
Start the game once. You may receive a crash to desktop (CTD) error; this appears to be some aspect of the mod completing installation and then making nice with Steam. Start it again, and it should run.
If you have been playing vanilla XCOM in a language other than the one you installed it in, switch XCOM to the installed Long War language via its properties in Steam.
Installation Notes
This mod will overwrite several game files and likely render multiplayer unplayable until you uninstall.
Mac and Linux versions are available via separate downloads.
The mod will not work properly on vanilla Enemy Within campaigns, so you'll need to start a new one. Campaigns are saved even if you uninstall, so you should be able to return to vanilla campaigns. Long War campaigns probably won't work well in vanilla.
If Firaxis/2K Games issues any patches to vanilla XCOM, it will overwrite and disable Long War, and almost certainly make the mod unplayable until the modders are able to update it. Unfortunately, turning off automatic updates to the game in Steam, via the game's Steam Library context menu ? Properties ? Updates tab, does not prevent patches from loading. Your savegames should be preserved, though.
If you want to use alternate game textures via TexMod, install them AFTER you fully install Long War.
If you install this mod over an existing version you won't be able to uninstall back to vanilla; to do so, you'll have to go to Steam and use the Verify Integrity of Game Cache option (under the game's Steam Library context menu ? Properties ? Local Files tab) to restore your game to its original settings. You should also do this if something goes wrong with the uninstall.
On Beta 9a and earlier, if this is your first time playing Long War, you should hit Alt+F10 once at the beginning of the game (once the first mission is underway) to reset your map cycler. This will be done automatically when starting a new campaign in Beta 10 and afterward.