We seek to demonstrate how Marx's integrated understanding of capitalism in general, which follows from his theory of the determination of value by labour-time, helps us to understand the particular question of knowledge-based production. Section one records the debate over the internal consistency of Marx's theory of value. Section two explains how Marx's conception of capitalism as the unity of a valorization process and a labour process shapes our conception of which activities are productive. Section three considers the relevance of Marx's definition of productive and unproductive labour to our understanding of knowledge-based production. Section four focuses on research and development in the context of Marx's theory of value. Section five explores the question of training/skills in our knowledge-based society, informed by Marx's concept of simple and more complex labour-power. We conclude, noting how George Lucas measures the value of 49 seconds of film on the imaginary planet of Mustafar.