Function keys that start with an are recognized in Insert mode. When this option is off, the cursor and function keys cannot be used in Insert mode if they start with an . The advantage of this is that the single is recognized immediately, instead of after one second. Instead of resetting this option, you might want to try changing the values for 'timeoutlen' and 'ttimeoutlen'. Note that when 'esckeys' is off, you can still map anything, but the cursor keys won't work by default. NOTE: This option is set to the Vi default value when 'compatible' is set and to the Vim default value when 'compatible' is reset. NOTE: when this option is off then the |modifyOtherKeys| functionality is disabled while in Insert mode to avoid ending Insert mode with any key that has a modifier.