The Rebel Alliance moved to Hoth after their victory in the Battle of Yavin. However, an Imperial probe droid discovered their base, then self-destructed upon being spotted (and shot at) by Han Solo and Chewbacca. The Rebels immediately began preparations to leave, but Darth Vader's Death Squadron, the 501st legion of the Imperial Army, Blizzard Force, arrived in time to intercept them, forcing the Rebels into a skirmish to cover their escape. Although the Empire won the Battle of Hoth by destroying the Rebel base and capturing many Rebel personnel and equipment, the Rebels didn't attempt a full-scale defense, but rather worked to stall the Empire's forces long enough to stage an effective evacuation, and to allow the deletion of compromising information about the whereabouts of the Rebel Fleet. Since the Rebels did evacuate vital leadership, personnel, and equipment, the Empire failed to do more than stall the Rebels' plans, and the Rebel Fleet remained elusive.
The action on Hoth features prominently in the opening of Star Wars Episode V: The Empire Strikes Back and is one of the Star Wars series' most memorable sequences.
Hoth is an example of the science fiction stereotype of a planet that has only one climatic zone. However, some Expanded Universe sources show that under-ice caves containing large lichen fields exist on the planet, on which Tauntauns feed. Echo Base is the Rebel Alliance base established after the Alliance evacuation of Yavin IV. The base, which was featured in the opening sequence of Star Wars Episode V: The Empire Strikes Back, is composed of a series of tunnels and caverns cut from the icy mountainside of the planet Hoth.
Echo Base was not designed with the means to repel an Imperial assault, but instead relied on its shield generator and its hidden location on a desolate planet in an unoccupied system to protect it from the Empire. Because of this most of its equipment and machinery were able to be taken apart and evacuated at a moment's notice, if the base was discovered.
When the Empire's probe droids found the base, the Rebels fought a holding action to give the transports enough time to evacuate. They used the base's planetary defense shield to prevent an Imperial orbital bombardment, and then used small airspeeders modified for the cold climate of Hoth, called Snowspeeders, and a small contingent of soldiers, to slow the advance of the Empire's AT-AT walkers. This holding action allowed the Rebels time to use Echo Base's Planet Defender Ion Cannon to open holes in the Imperial blockade, allowing many transports and their X-wing escorts to escape.
Echo Base suffered a series of attacks by the shaggy and carnivorous wampas soon after Commander Skywalker's encounter with one of the creatures. This is not shown in Empire Strikes Back, but was described in the accompanying novelization.