How do you mute players in Battlefield 3?

In Battlefield 3, to mute other players open the in-game menu (Default: Start/Esc), select 'Team & Squad' and change 'VoIP' to 'OFF'.

This will prevent voice communication to and from the player's own team and squad. Setting this option to 'Team' will allow voice communication between the player's own team (including squad), setting this option to 'Squad' prevents communication between the player's team, but allows communication between their own squad.