The Nightfall Pact is the treaty governing the relations of the Serenna clans.

Space controlled by clans signatory to the Pact, and the clans themselves, are also generally referred to as the Nightfall Pact.

Since the Serennae are highly isolationist by nature and generally avoid, or try to get rid of, other Serennae, the history of the clans is filled with cold wars and long-held grudges. As Serenna technology advanced, it became clear that some sort of formal process would be needed to keep things under control and ensure a degree of cooperation. The leaders of the major clans agreed to a treaty, under which clans would refrain from outright attacks on each other, and which provided mechanisms for dispute resolution and dealing properly with any business concerning the Serennae as a whole. This was the Nightfall Pact.

Over time, the Pact has grown into a formidable document. Every major agreement between signatory clans is codified into the Pact, ensuring that it is taken seriously - to breach the Pact is to go to war with all the clans. These agreements range from technical standardisations (vital with the rise of Serenna spaceflight) to alliances that have endured for millennia. Much like the clans' starships, like their DNA itself, the Pact tells a story of every Serenna who has come before.

Pact business is decided upon by the Council of the Pact, made up of representatives from each signatory clan. The Council is led by the Voice of the Pact, whose word is final.

Council meetings are held at the Nightfall Embassy.

As well as governing relations between the clans themselves, the Pact also acts as a unified front for clan relations with the other governments of the galaxy. Although the clans - and indeed individual systems, planets, starships, and Serennae - can practice low-level diplomacy on their own terms, important issues are handled through the Council of the Pact, and agreements with other governments are also written into the Pact itself. This includes recognition of the territory claimed by the clans. Accordingly, such space is considered by outsiders to be claimed by the Nightfall Pact. This territory is generally located in the Spinward, Cawdren Heath, and Genesta Corus regions.

Pact space is divided into several main regions, each belonging to one of the major clans. Buffer zones exist between these regions, which are considered to be governed directly by the Council of the Pact. These zones are used to transit through Pact space without having to enter the space of any particular clan, which would add substantial diplomatic effort to any journey.