The Pro Micro is similar to the Pro Mini except with an ATmega32U4 on board.
The USB transceiver inside the 32U4 allows us to add USB connectivity on-board and do away with bulky external USB interface.
This tiny little board does all of the neat-o Arduino tricks that you're familiar with: 4 channels of 10-bit ADC, 5 PWM pins, 12 DIOs as well as hardware serial connections Rx and Tx. Running at 16MHz and 5V, this board will remind you a lot of your other favorite Arduino-compatible boards but this little guy can go just about anywhere.
NB. There is a voltage regulator on board so it can accept a voltage of upto an ABSOLUTE MAXIMUM of 12.00VDC, but only on the RAW pin and NOT on the VCC. The VCC is a 5V output. DO NOT SUPPLY 12V TO THIS PIN. (To be safe rather use a maximum of 9VDC to the RAW pin)