As part of Configuraton Change Notification and Logging feature, Cisco IOS stores the most recent configuration commands in a circular buffer and (optionally) sends them to syslog streams.

This feature is configured under the archive configuration mode with the log config command, which brings you to yet another configuration mode where you can fine-tune the parameters (they are obvious, on-router help is sufficient), for example:

archive
 log config
  logging enable 100
  notify syslog
  hidekeys

After you've enabled configuration command logging, you can use the show archive log config all command to inspect the logging buffer. You can also display commands entered in a particular session or by a selected user.

If you've configured notify syslog, every configuration command also triggers a syslog message similar to this one:

3d03h: %PARSER-5-CFGLOG_LOGGEDCMD: User:console logged command:interface loopback 0

Note: This feature logs only the configuration commands, if you want to log all commands, use TACACS+ or Embedded Event Manager.