The present chapter intends to explore the genesis of the Theory of Law, starting from the meaning of General Theory of Law, within the internal History of Modernity, and emphasizing its relevance to the global History of Legal Thinking. It will involve an approach to the historical origins, rational autonomy and method of Legal Theory, concerning the transition from the period of predominance of Jusnaturalism to Juspositivism, and the consolidation of the Science of Law. Therefore, the foundational role of Legal Theory within the Modern concept of Law is exposed, concerning the rational links between Law and Legal Thinking. And, consequently, a critical approach to the subsequent developments points out the overcoming connections within Legal Theory.