Earth Defense Command is a human-run military organization.
The Transformers cartoon continuity
The Earth Defense Command was formed in 2003 as part of a cooperative human/Autobot effort. When the Cosmic Rust virus critically struck the Autobots later that year, the EDC kicked off the Binaltech Project to shore up its defenses.
When Galvatron was hurled out of Unicron by Rodimus Prime in 2005, rather than immediately crashing onto the planet Thrull, he instead hurtled toward Earth. Landing in Tokyo, Japan, the Decepticon leader's impact decimated the city and scattered his Unicron-mutated cells throughout Earth's atmosphere.
Following this catastrophe, the EDC was reborn as an organization dedicated to driving all Transformers off Earth. The organization built an anti-electron field (previously referred to as an Energon field) to make the planet uninhabitable to Cybertronians, and created a team of 48 transforming robots known as Autroopers to combat any Transformers that remained, recruiting young women who had been infected with the cells and gained Kiss Player fusion abilities to partner with them.
Although the organization ostensibly defended humanity from attacks by Legion (monstrous creatures resulting from the fusion of Galvatron's Unicron-mutated cells with ordinary objects and lifeforms), it was secretly using those same cells to create its Autrooper forces. Under the command of Hitoshizuku Amaō, it built a facility called the Genital System beneath its Tokyo-based headquarters. Inside this secret chamber, Galvatron's headless body was imprisoned and terrible experiments were conducted using captured Legion remains and EDC Kiss Players. The goal of these experiments was the resurrection of Amaō's daughter, who had been killed in the Tokyo disaster.
A joint attack by Optimus Prime and Marissa Faireborn, Hot Rod and former EDC Kiss Player Shaoshao Li, and current Kiss Player Atari Hitotonari and her Ne-04 Autrooper partner exposed the Genital System facility. Amaō was killed, Galvatron was restored and launched into space, and the anti-electron field was taken down.
The EDC was reformed and returned to its original policies. Together with Autobot leader Ultra Magnus, it created the Kiss Players singing group, which toured the planet to promote peace and good will between the two species.
The Transformers cartoon
The Earth Defense Command is a joint human/Autobot military organization dedicated to the protection of Earth and its solar system. It was founded at some point before 2005, and by that year at least three space stations had been constructed (one in Earth orbit, one at Pluto, and a third near Goo#8739). This defense is augmented by a Mars land base, as well as several space vessels that allow quick transit throughout the solar system and beyond.
The Earth orbital station observes traffic to and from the planet, with the authority to call out Autobot and/or human military assistance. The Pluto station served much the same function, its proximity to a warp gate making it a first line of defense against hostiles from non-Solar worlds. Unfortunately, even with its advanced technology, this battle platform was destroyed in a matter of moments by Galvatron and his lieutenants. It is unclear whether the Earth base would survive a similar attack. In 2006, the deep-space station near Goo was demolished by death crystals, even though (according to Grimlock) it was built out of the strongest metal in the galaxy.
On a smaller scale, powerful technology (most likely Cybertronian) has also been incorporated in land and air vehicles. An EDC car kept up a decent fight during a high-speed road duel involving two Stunticons and Rodimus Prime. The car was armed with a roof-mounted blaster (not to mention incredible crash protection and recovery systems). Also, a similar vehicle has been seen flying despite a lack of suitable wings or the noise of conventional propulsion - just like a Transformer.
The hierarchy of the EDC is unclear, although it appears that the Autobots may be ultimately in charge. It's also unclear whether any Autobots are technically considered EDC officers. All the humans wear white uniforms with blue trim; no Autobots have been seen changing their paint jobs to fit in.
The only EDC officer whose name we know is Marissa Faireborn.
Dreamwave Generation One comics
The EDC was founded by Nathaniel Faireborn to deal with extra-terrestrial matters shortly after the emergence of the Transformers in the mid-eighties. Its base of operations is located at Area 51. Faireborn's intention was to better Transformer/human relations, but the damage the Transformers conflict caused on Earth, along with an Army General with a last name of Witwicky and a talent for hiding from the camera/reader, often made this difficult.