The Arduino Micro is a microcontroller board based on the ATmega32u4. It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a micro USB cable to get started. It has a form factor that enables it to be easily placed on a breadboard.
The Micro is similar to the Arduino Leonardo in that the ATmega32u4 has built-in USB communication, eliminating the need for a secondary processor. This allows the Micro to appear to a connected computer as a mouse and keyboard, in addition to a virtual (CDC) serial / COM port. It also has other implications for the behavior of the board; these are detailed on the getting started page.
Input Voltage (recommended):7-12V
Input Voltage (limits):6-20V
Digital I/O Pins:20
Analog Input Channels:12
DC Current per I/O Pin:40 mA
DC Current for 3.3V Pin:50 mA
Flash Memory:32 KB (ATmega32u4) of which 4 KB used by bootloader