There are two rulebooks for the BA Cosmo Cup. You will need both for either division you enter.

The Division Rulebook will share with you the essential rule differences between each league, such as roster limits, war times, troop restrictions and other essential information. All participating players should read this rulebook to understand the main timings and rules that apply to them.

The Master Rulebook includes all other rules that are set from league to league. These include negotiation rules, penalties, and other crucial information. We don't expect players to know all these rules, but we expect any representatives for teams to understand these rules to a competent standard. 

You can find links to both below, as well as the standings link for LeagueUtils.