| Sumario: | Even though real numbers are such an important tool and model in mathematics, no strict description is provided in many situations. The aim of this paper is to fill this gap by presenting some of these constructions. After giving a synthetic definition of the real numbers and a precise definition of rational numbers, we present the classical constructions of the real numbers proposed by Cantor, Dedekind and Weierstrass. Indeed, these were the first successful descriptions of the field of the real numbers. Finally, we explain the definition given by Rota and three other mathematicians, showing that this work can also be carried out by an algebraic approach.; Zenbaki errealak funtsezko tresna eta oinarrizko eredu dira matematikaren arlo anitzetan. Hala ere, sarritan definizio zorrotzik emateari uko egiten zaio. Historian zehar aurkeztu diren zenbait aukera azalduz, hutsune hau betetzea da artikulu honen xedea. Bide honetan, zenbaki errealen definizio sintetikoaren eta zenbaki arrazionalen deskribapen zorrotzaren ondoren, eginbehar hau modu zuzenan gauzatzen lehenengoak izan ziren Cantor-en, Dedekind-ren eta Weierstrass-en eraikuntza klasikoak aurkeztuko ditugu. Azkenik, Rota eta bere lankideen lana azalduko dugu, bide batez, beste ikuspuntu batetik, aljebrarena hain justu, definitzerik dagoela erakutsiz.
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