In the years leading up to 2063, humanity has begun to colonize other planets. Lacking FTL technology, this is accomplished by taking advantage of transient but
predictable, naturally-occurring wormholes. Without warning, a previously unknown alien species, the "Chigs", attack and destroy Earth's first extra-solar colony and
then destroy a second colony ship. The bulk of the Earth military forces sent to confront the Chigs are destroyed or outflanked, in part because the Chigs have some
form of FTL, affording them greater freedom of movement (although this technology appears limited, and the Chigs also primarily utilize natural wormholes). In desperation,
unproven and under-trained outfits like the 58th "Wildcards" are thrown against the Chigs. The Wildcards are the central focus of the series, which follows them as they
grow from untried cadets into veterans. Although the unified Earth forces come under the control of a reformed United Nations, the UN has no armed forces of its own and
therefore navies such as the U.S. Navy and the Royal Navy operate interstellar starships.
The Space: Above and Beyond milieu includes an underclass race of genetically engineered and artificially gestated humans who are born at the physical age of 18, and are collectively
known as In Vitroes or sometimes, derogatorily, "tanks" or "nipple-necks". The In Vitroes have replaced the previous underclass, the artificial intelligences known as
Silicates.
These human-looking androids, referred to as "walking personal computers", have rebelled, formed their own societies, and wage a guerrilla war against human society. The
Silicates are also suspected of having some involvement with the Chigs.