This book contains details of the 29 worlds that have so far been colonised by people from Earth. They are organised by where they are - Core, the French Arm, the Chinese Arm and the American Arm - and each receives an essay-style presentation that includes astronomical data about the complete system, details about the colony world itself (with special note taken of those natural and environmental characteristics that could make it a challenge to live there) and wide-ranging backgroud and historical material covering its development from discovery to the present day. The intention is to provide the referee with sufficient information to allow the characters to visit any world, and have adventures thereon.
The only colony in Core (i.e. near to Earth) is Tirane, a planet in the Alpha Centauri system. It was the first world outside of our Solar System to be visited and colonised, and still serves as a jumping-off point wherever else in the galaxy you might wish to go. It is very Earth-like, capable of supporting Earth flora and fauna whilst people from Earth can eat native plants and animals (and, of course, vice-versa!), and is now well-populated by people from many nations on Earth.
Next, we take a look at the French Arm. Not everyone here comes from France, however, but they are in the majority (remember the dominance of France in the 'future history' in the core rulebook?)... although there are a lot of Bavarians there as well, due to a strange (and as yet unexplained) tendency for French probes to get lost whilst identical Bavarian ones operated as intended. There's a map, a cunning attempt to present 3D space in two dimensions - although the formula for calculating the distance between any two stars is enough to daunt all but confident mathematicians! Some entries include adventure ideas, others highlight places of interest that a tourist might want to visit... it's thought, however, that it might take a lifetime to visit all the planets described in this book, so choose wisely where you want to go! Many worlds have colonies from several nations and they do not always coexist in complete harmony.
The Chinese and American Arms follow, with similar diversity including some truly fascinating native wildlife. Most worlds are still actual colonies, owing aliegiance to their 'home' government back on Earth, although the distances involved means that they all have to be to at least some extent self-governing. Those who revel in the concept of different ways of doing things will find plenty here, the 'what-if' that makes for good science-fiction is well represented amongst the 29 colonised worlds.
It's a fascinating glimpse at a wide range of well thought out worlds, any of which could provide a place to visit or even a home to your party, with plenty for them to do whilst there... and virtually all is generic enough rules-wise that you don't need to be playing 2300 AD to make good use of them.