From the back cover:

Welcome to the Core!

"First time? Don't worry - you're bewildered, but we'll help you cope! Try one of the orientation memoplexes - they'll stop you saying or doing anything too clumsy, no matter how far out on the Fringe you come from. Try not to stare! That's an autotroph. Yes, their skin is green. And you'll soon learn not to bump into people - it's a dance when we all live so close together, you see? And the rules change from arcology to arcology, world to world, day to day.
Now, let's get you some clothes. And some new skin, hair, and eyes - the ones you're wearing are... well, rustic. Oh, where to start! There's so much to learn! Now, what gender would you say were today?"

The Core Worlds... the ancient homes of humankind. Settled thousands of years ago, in a time so distant it would have been totally forgotten if not for the planetary senitences. Cultures and traditions of dizzying exoticism, united by one great idea: that for millenia they've all been members of humankind's greatest civilisation.

The Core Worlds Sourcebook introduces the vast and teemingheart of the New Commonality of Humankind, opening up this exotic region of Human Space for your Mindjammer game. It includes:
- Background and histories of a whole sector of space.
- Transect schematics and starmaps.
- Details of planets, cultures for creating Core Worlds characters.
- Deep background on Old Earth and Manhome, including maps of Old Earth, Green Moon, and Old Mars!