This work analyses the evolution of the separation of powers, in accordance with the most ancient thinkers of this theory and its first adoption in the Constitution of the United States of America that, since some modifications, it has allowed the intervention of the three powers of the State between them, in certain cases. The case of Colombia offers a special interest because article 113 of the Constitution of Colombia of 1991 allows the “harmonious collaboration” (colaboración armónica in its Spanish translation) between the powers of the State and the autonomous agencies, and article 116, that enables the law, exceptionally and under specific circumstances, to attribute quasi-judicial functions in specific matters to the administrative agencies. The separation of powers is not as rigid as it might appear as neither that exceptional because, as it is shown in this investigation, the administrative agencies that are empowered to make decisions with a judicial nature are more numerous than generally expected. The results of this investigation are: (i) the identification of eleven administrative authorities that exercise quasi-judicial functions; (ii) these mixture of functions is explained by the principle of harmonious collaboration between powers in accordance with constitutional jurisprudence; (iii) the decisions of these administrative authorities have been recognized by the jurisprudence as authentic judicial sentences. The theory of separation of powers has evolved over time and the number of administrative authorities that have assumed quasi-judicial functions is increasing for reasons of greater efficiency and specialty.
