Horn is best known for his book Liber Horn, compiled in 1311. Besides coroners' reports and other mundane matters, Liber Horn contains some of the earliest and most reliable versions of early English laws, including certain Statutes of uncertain date and an annotated copy of Magna Carta of 1297.[5] Horn is also thought to have compiled and edited La somme appelle Mirroir des justices: vel Speculum justiciariorum (translated variously as The Mirror of Justices or The Mirror of Justice).[6][7][8]
As a legal scholar, Andrew Horn's literary achievements consisted largely of compiling, editing, transcribing, and annotating statutes, pipe rolls, chronicles, and other official documents. This has resulted in a problem of attribution, since it is not always clear to what extent he acted as author or editor.