Marxist (later, Marxian) economics descends from classical economics and it derives from the work of Karl Marx. The first volume of Marx's major work, Das Kapital, was published in German in 1867. In it, Marx focused on the labour theory of value and the theory of surplus value which, he believed, explained the exploitation of labour by capital. The labour theory of value held that the value of an exchanged commodity was determined by the labour that went into its production and the theory of surplus value demonstrated how the workers only got paid a proportion of the value their work had created.
