*Note – Before you can install custom ROM, you need to root your Galaxy S4.
What is rooting and why should you root your Galaxy S4?  Please see this video explanation. Don’t know what is a custom ROM? See What is An Android Custom ROM.

Rooting Galaxy S4

For Galaxy S4 GT-i9500 Exynos Octa-core, AT&T SGH-i337, Sprint SPH-L720, and T-Mobile SGH-M919, and Korean (E300S, E300K, E300L) see How to Root Galaxy S4 with CWM.
For Galaxy S4 GT-i9505, T-Mobile Galaxy S4 SGH-M919 Sprint Galaxy S4 SPH-L710, Canadia Galaxy S4 (Bell, Rogers, Telus), US Cellular Galaxy S4 SCH-R930, please see How to Root Galaxy S4 with TWRP
For Galaxy S4 Qualcomm versions like AT&T SGH-i337, T-Mobile SGH-M919, Sprint SPH-L720, Verizon, US Celluar, Rogers, Bell, or Telus, please see How to Root Galaxy S4.
For AT&T Galaxy S4 Active, see How to Root Galaxy S4 Active!
*Note – Some models have multiple methods of rooting and some only have one root method.  CWM or TWRP root method involve installing custom recovery, which is recommended so you can install custom ROMs and also backup/restore ROMs.
For unrooting Galaxy S4 completely back to stock and unvoid your warranty, see How to Unroot Galaxy S4 and Remove Root!

Compatibility Notes on S4 Models

You can install any GT-i9505 ROMs on your T-Mobile/Canadian Galaxy S4.
For Korean S4 (E300S, E300K, E300L), see here for compatibility notes.

Custom Recovery Tutorials for Galaxy S4

If you rooted your Galaxy S4 with custom recovery such as CWM or TWRP, here’s some tutorials you will want to follow.
If you have newer AT&T or Verizon Galaxy S4 4.4.2, you need to use SafeStrap Recovery instead!!!
First, make sure you make a backup ROM after rooting, see How to Backup/Restore ROM on Galaxy S4 with Root.
If you want to install a custom ROM, see How to Install Custom ROM on Galaxy S4.

Wifi Tether on Galaxy S4

For AT&T Galaxy S4 SGH-i337, see How to Wifi Tether on AT&T Galaxy S4.

Other Useful Galaxy S4 Tutorials

Did you DROP your Galaxy S4? Or perhaps dropped it in water and some parts are not functioning correctly? Here’s a step-by-step tutorial on How to Disassemble/Assemble your Galaxy S4 and also How to Replace Screen Glass Only on Galaxy S4!
Need Flash Player?  Here’s How To Install Flash Player on your Galaxy S4!
Want to run T-Mobile on your AT&T Galaxy S4?  See how to enable T-Mobile AWS Bands on your AT&T Galaxy S4.
Need to unlock SIM on your AT&T or T-Mobile Galaxy S4?  See how to unlock SIM on AT&T/T-Mobile Galaxy S4!