Pedro Dorado Montero was one of Spain’s most relevant authors. He contributed to modern Criminal law and Penology with a very unique theory: the Protective Law for Criminals. In a time when neoclassical penal theories and new positivist theories clashed, Dorado Montero’s proposal served as a bridge between the criminal law conceptions of the 19th and 20th centuries. In order to explore his role in the introduction of positivism within Spain and the subsequent success of this trend, this book addresses several aspects. The first three analyzed are his scholarly career, the historical and international context in which he lived, and the various European and other international influences he was exposed to. On this basis, two major points are then discussed. Firstly, Dorado Montero has been traditionally included within the movement known as correccionalismo. However, his legal-philosophical and criminal thought indicates otherwise. It seems to lie closer to positivism than to neoclassical positions. This research aims at challenging the accuracy of the ‘eclectic’ label which traditional historiography has applied to him. In turn, Dorado Montero described a reality in which every moral value and legal representation was a mere product of mankind’s imagination. Man is responsible for the elaboration of morals, law and culture in his own mind. Thus, for him, there were as many moral and legal orders as there were human beings on the planet. Such a claim is polemic even today. Unsurprisingly, the author received criticism from both neoclassical and positivist schools. Thus, the existence of a ‘Doradian positivism’ is explored. Despite the growing interest in these topics over the last few decades, Dorado Montero has somehow been overlooked – even though his Derecho protector de los criminales described the criminal law of the future as well, one that will have to face the new neurological, medical, psychological and genetic challenges of our time.