The laws of Hywel Dda are mainly contained in three collections of manuscripts setting out Wales's native and distinct legal system. Scholars agree that the most developed version is Llyfr Iorwerth, the Book of Iorwerth, which dates from the thirteenth century. It was named after a lawyer, Iorwerth ap Madog, who complied a llyfr prawf, or test book, which contains all of the core texts that people needed to know in order to become a justice. The Book of Iorwerth also contains the laws of court and more general laws of the land.

Setting out the laws of a country is vital to provide certainty and protection for citizens and their environment, to prevent arbitrary decisions and to ensure people know their rights and their obligations. Our ancestors seemed to have understood this better than we do. As we are told in Llyfr Iorwerth, they kept the law under review, or, in its words, they

'examined the old laws, and some of them they allowed to continue, others they amended, others they wholly deleted, and others they laid down anew'.