The Referendum stands as one of the most traditional institutions of direct democracy in western constitutionalism. This article aims to lay out a comparative study on how that institution is nowadays regulated in European States, as well as its role in Spanish law. This text shall conclude with a summary of the doctrine on how the institution of Referendum fares in 21st century constitutionalism in Spain, showcasing the main arguments both in favor of and against it.El Referéndum es una de las instituciones de democracia directa con mayor tradición en el constitucionalismo occidental. Este artículo pretende plantear un estudio comparado de las distintas regulaciones actuales del Referéndum en los Estados europeos, así como su papel en el D...