The authors prove the existence of the isoperimetric set in Carnot groups, that is the existence of a set \(E\) minimizing the intrinsic perimeter \(P_G\) among all measurable sets of prescribed Lebesgue measure \(v\). The authors give also some regularity result of this set; they prove that the set \(E\) has a unique reduced equivalent set \(E_1\), with \(E_1\) open and bounded, \(\partial E_1\) Ahlfors regular and such that \(E_1\) satisfies the \(B\)-condition (i.e., there exists \(C>0\) such that for any ball \(B\) centered on \(\partial E_1\) and radius \(r\leq1\), there exist two balls \(B_1\) and \(B_2\) with radius \(Cr\) such that \(B_1\subset E_1\cap B\) and \(B_2\subset B\setminus \bar E_1\)), with constants that do not depend on \(E\) (they depend only on the dimension and on the volume \(v\) of \(E\)). In the last section it is also proved that in the special case of Heisenberg groups the reduced isoperimetric set \(E_1\) is a domain of isoperimetry, that is a relative isoperimetric inequality on \(E_1\) holds.