This is a fan-made edition of Warhammer 40.000.

It is intended for people already familiar with the original rules for 6th or 7th edition. The presentation of the rules is not appropriate for new players.
I will not explain the general principles, like what a blast marker is or how a re-roll functions or how to take a characteristic test.

For the easiest way to familiarize yourself with the changes, I recommend reading the sections exactly in the order they are listed in, from top to bottom.

While this document reads more like an errata right now, it should be treated like a new, separate edition of 40k, building upon the core mechanics of 3rd, 4th, 5th, 6th and 7th edition, essentially familiar but put together in a new way. As with other edition changes since 3rd, the current Codexes remain valid with some minor errata required here or there to cover strange rules interactions, but as with any re-jigging of the core rules, you will discover that the usefulness of many units has changed, either for better or worse.

It should be noted that no attempt was made to balance different factions through core rule changes. All changes to the core rules were made with the intention to produce a smoother and more exciting playing experience. Balancing the factions should be a matter of Codex tweaks, not core rule tweaks.