Abstract.  In this paper I outline various different objects of investigation that may be picked out by word “law” (or its cognates). All of these objects must be investigated in an integrated way before one can provide a complete philosophical explanation of the nature of law. I begin with the distinction between laws (artefacts) and law (the genre to which the artefacts belong). This leads me to the distinction between the law (of a particular legal system) and law (the genre of artefacts). Then I discuss the contrast between law (the genre of artefacts) and law (the practice). Finally I comment on legality as the name of an ideal for laws and legal systems to live up to. I commend H. L. A. Hart's explanation of the nature of law for investigating these various objects in an integraed way, while nevertheless respecting the distinctions among them. I also criticise some of R. M. Dworkin's work for failing to respect the same distinctions.