connect arduino mega 2560 to arduino uno rev 3

Hello everyone! Is it possible to connect arduino mega 2560 to arduino uno rev 3? Let us say I am going to use mega as the main controller. If yes, I wish you can tell me how. Thank you

However you want. I prefer serial, but there is always SPI or two-wire interface. Actually communicating is up to you. 8^)

Can be simpler too - just writing an output pin hi or low. Evertytime the Uno sees the pin change it does something,
Really depends what you want the Uno to do.
If its more complex, like turn on LED #4 for 7 seconds, then some form of serial comm's would be good - UART, SPI, I2C, software serial.