This thesis investigates the German cameralist Johann Heinrich Gottlob von Justi's economic theories and policy proposals about manufacturing, innovation, technological progress, and people's industrial spirit and skills. It contextualises Justi's theories and policy proposals about these topics with the political economy of absolute monarchy represented by the economic thought of Giovanni Botero and the late seventeenth-century Austrian cameralists. It also contextualises Justi's theories and policy proposals with the political economy of enightened absolutism represented by the natural law theory of Christian Wolff and the thought of the "Industrial Enlightenment" in the early modern period. This thesis challenges and revises two kinds of prevailing interpretations of Justi's economic thought: one believes that Justi's economic thought aimed at sheltering the rent-seeking of monarchs and cameralists, and the other thinks that Justi's economic thought advocated a free market with the minimised and reactive state intervention. This thesis argues that Justi's economic theories and policy proposals were primarily concerned with not rent-seeking but how to create an economy fitting his definition of public happiness, namely an economy having a large output of goods, strong demand, high productive powers, prevented the polarisation of distribution, and provided citizens with abundant chances to work to earn their comfortable lives. This thesis also finds that Justi theorised the phenomenon of the economic expansion driven by the development of new manufacturing and by the introduction of product and process innovations and the progress of technology and science, and that Justi proposed a set of policies based on his theoretical understandings and expected to create the economy of public happiness through building diversified manufacturing sectors and stimulating innovations and technological progress. This thesis also shows that the economic model proposed by Justi was an economy under the strong leadership of the state especially in the aspects of realising the evolution of industrial structure and promoting the progress of industrial technologies. Justi's model of "free market" was not a market free from proactive and visionary state intervention but a proper division of labour between state intervention and private initiative. In general, this thesis argues that there was a set of theories and policy proposals deserved to be named "the eighteenth-century entrepreneurial state" in Justi's economic thought and that Justi represents a long-forgotten but noteworthy forefather of economic modernity.