How can I enable line wrap on word boundaries only in Emacs?

M-x toggle-truncate-lines disable allows you to disable visually line breaking.

M-x auto-fill-mode + M-q allows you to word wrap for real a pre-existing paragraph.

Add this to your init file:

(setq-default word-wrap t)

Alternatively, press C-h vword-wrap in Emacs and follow the "customize" link near the end.

If you want to emulate the behavior of an editor like Notepad, you might want to turn on visual line mode. While setting word-wrap will cause line wrapping at word boundaries, any action you take on a line (e.g., moving up/down or killing) will still respect the newline character. Visual line mode will treat each display line as though it had a newline at the end.

(visual-line-mode t)

Line to add in .emacs file:

(global-visual-line-mode t)

I discovered longlines-mode only recently (I think I was spelunking through the Emacs Info documentation). It wraps as you would expect in other UI editors' word-wrap feature. It's especially useful when I'm reading or writing free text with no newlines (a la Microsoft Word) without the ugly mid-word wrapping that happens when you use M-x toggle-word-wrap.

See LongLines.

My configuration:

(setq longlines-wrap-follows-window-size t)
(global-set-key [(control meta l)] 'longlines-mode)