This book, first published in 1988, is an English translation of the sixteenth-century Spanish treatise Tratado de Cuentas or On Accounts by Diego del Castillo. The broad purpose of this work is to make this treatise and the issues it raises in accounting history better known. Despite its importance to the field, the Tratado has until this point been relatively inaccessible. The Tratado is a legal treatise with legal implications – accounting activity has always had social consequences, and as a result, accounting practices have been subject to and shaped by legal constraints throughout their history. This work makes clear the important relationship between law and accounting.