Articles about master and slave switches
How can I wire a 3way dimmer switch to one of the switch locations? Dimmer Switch Wiring Connections, Installing Multiple Dimmer Switches, Types of 3Way and 4Way Dimmer Switches.
Understanding 3-Way Dimmer Switch Compatibility – When using two or more dimmer switches they must be compatible with each other. Some brands will require you to have Master and Slave units, such as Lutron.