From the back of the book:
This Space: 1999 Core Rulebook offers everything you need to play adventures of your own in the far reaches of the frontier of space!
Extensive detail about life on Moonbase Alpha, its locations, departments and how the Alphans spend their time.
A complete rules system using the award winning 2d20 game engine from Modiphius Entertainment. This system has been adapted specifically to run Space: 1999 but remain compatible with any other 2d20 game.
Create your own character or play one of the iconic series characters.
Advice and rules for running the game and creating new adventures of your own, whether you are an experienced Gamemaster or a complete novice.
A host of non-player characters with systems and advice for creating new and exciting people and aliens to encounter on your journey into space.
A ready-made adventure “Project Arrow” to begin your campaign, where the people of Moonbase Alpha launch one last, desperate attempt to reach Earth.