This is an FAQ that will be updated often, please leave your questions in the comments section!
If you don’t know what rooting means, please watch this video first:
Don’t know what is a custom ROM? See What is An Android Custom ROM.
IMPORTANT: PLEASE DO NOT FLASH i9300 ROMs on U.S. or Canadian Galaxy S3 variants or VICE VERSA! Please read the title of post, they will specify the model number of your Galaxy S3!
Note: Galaxy S3 on this site refers to GT-i9300 International models if not specified, which is the original Galaxy S3.

General Tutorials

Root Guide for GT-i9300

Root Guide for T-Mobile Galaxy S3 SGH-T999

Root Guide for AT&T Galaxy S3 SGH-I747

Root Guide for Sprint SPH-L710

Root Guide for Verizon SCH-I535

Got a Korean S3?  We don’t support Korean S3 models but you can check here.
Need Help? Best way to reach me is on Twitter for the fastest response!
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Galaxy S3 Reference
You will need a rooted Galaxy S3 to install all ROM/kernels.
NOTE: PLEASE ONLY INSTALL ROMS INTENDED FOR YOUR VERSION OF GALAXY S3! Otherwise you WILL BRICK YOUR PHONE and I will not be responsible!
First time to rooting and custom ROMs? Please see our Galaxy S3 Root FAQ FIRST!