Resistance

The Resistance is the remaining human forces still fighting the Combine.

Resistance Structure
The Resistance appears to have no apparent command structure and just appears to be militia like cells with its own independent commander. The Resistance in City 17 is led overall by Doctor Kleiner and Doctor Eli Vance who also control the Rebel's scientific research into teleportation. The operations that the Resistance conducts in the field is led by Barney Calhoun and Alyx Vance. Gordon Freeman offers leadership near to the end of Half Life 2, leading small squads of resistance fighters against the Combine.

The exact size of the Resistance is not known, although given City 17's size it is safe to say that there are at least 12,000 soldiers. There is also a Civilian Militia force, members who have not fully gathered rebel equipment such as proper clothing and equipment and just instead use a weapon are seen near the beginning of the game Half Life 2 whom controls the Underground to get refugees out of the city.

This is evident that there is close ties with the actual Resistance Army and the Civilian Militia.

Resistance Weaponry
The Rebels use whatever armaments are available to them. The Rebels have been seen to use Handguns, MP7 Submachine Guns, Overwatch Pulse Rifles, Shotguns and Rocket Launchers. Resistance soldiers have also been armed with, at some point a Crossbow and although not a "member" of the Resistance, Father Grigori uses an ornate Winchester Rifle.

The Rebels use two types of vehicles, a Scout Car and an Airboat. Although not armed until Freeman reaches a small Rebel hideout, the Airboat is a versatile vehicle used to ferry rebels across the waterways. The Scout Car was built by Eli Vance and armed with a Tau Cannon to transport him around the countryside. Why he would transport himself around the countryside, given its increasing danger is not known.