How do I indent multiple lines at once in Notepad++?

It works fine for my v. 5.4.5 of Notepad++. I just select multiple lines and press TAB.

If you want TAB to be replaced by SPACE than you need to go Settings > Preferences and select Edit Components tab. Next check Replace by spaces check box in Tab Setting section.

Update: In a newer version of Notepad++ this option is in Settings > Preferences > Language section.

The problem was with the QuickText plugin. After removing it, indent worked as normal.

The problem with the new version of QuickText seems to be that it is set to react to the TAB key. Previously it was set to use CTRL-ENTER. If you change the key combination in the shortcut mapper then your TAB key should start working again, and QuickText should also work (with whatever new key you've assigned).

Capslock + Tab to indent multiple lines at once. Highlight the text first.