How can I get control+left arrow to go back one word in iTerm2?

bash

Just add the following to ~/.inputrc:

"\e[1;5D": backward-word
"\e[1;5C": forward-word

See this archived Wiki post for some more explanation. If you want to use the alt key instead for word-to-word movement (like default OS X behavior), use:

"\e[1;9D": backward-word
"\e[1;9C": forward-word

zsh

zsh by default does not use the readline library and therefore won't read ~/.inputrc. To get the same functionality, you could add the following to your ~/.zshrc – this again would use the alt key:

bindkey -e
bindkey '^[[1;9C' forward-word
bindkey '^[[1;9D' backward-word

See this documentation for more about the built-in zsh line editor (zle).

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Why is this? You've set up your profile to use the Xterm defaults:

This is why you'll need to "catch" this sequence and tell readline what to do.

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If the above still doesn't work and you are using OS X 10.9 (Mavericks) or there abouts, you probably need to disable the global Mission Control shortcuts which prevent Control+arrow keys from reaching iTerm, even if Mission Control itself is disabled. You can do so from System Preferences → Keyboard → Shortcuts → Mission Control:

Working solution for zsh. Simple, straightforward, out-of-the-box.

1. Goto: ⌘, Preferences → Profiles → Keys → Keyboard Behavior

2. Load Preset: Natural Text Editing

I fixed it this way:

In top menu; go to

Profiles 
-> Open profiles... 
-> Edit profiles... (button) 
-> Keys (tab) 
-> Load Preset... (dropdown) 
->  Choose "Natural text editing". Done! :-)