The Arduino Mega 2560 is a microcontroller board based on the ATmega2560. It has 54 digital input/output pins (of which 14 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Mega is compatible with most shields designed for the Arduino Uno, Duemilanove or Diecimila.

The Mega 2560 is an update to the Arduino Mega, which it replaces.

Additional features coming with the R3 version are:
- ATmega16U2 instead of 8U2 as USB-to-serial converter
- 1.0 pinout: added SDA and SCL pins for TWI communication placed near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allows the shields to adapt to the voltage provided from the board, and the second one is an unconnected pin that is reserved for future purposes.
- stronger RESET circuit.