Legislation may be by deliberation of a legislative body (parliament, congress, council, etc), or by fiat or decree of a ruler, or by public referendum, or various combinations thereof.  Regardless of how the laws of a place get written, every nation has a Supreme Law Court, which is also a temple of Pwyll, established by the Guild of Law, to which all national laws must be submitted to determine that they conform to the will of Pwyll, namely that laws shall benefit the general welfare of the people and that power shall be balanced.

Local laws and ordinances do not need to go through such scrutiny before passing, but if they are challenged, then they will be so examined.

For an example of an Aeldrethian legislative process, see The Navigators: Government of the Isles.