A theoretical study of the hydrogen peroxide-water (HPW) complex is presented. We analyze the ab initio quantum-mechanical calculations at the Hartree-Fock (HF), Møller-Plesset (MP2, MP4) levels of theory. Linear, cyclic, and transition state structures were determined. Correction for the basis set superposition error (BSSE) was taken into account by applying the counterpoise procedure. The 6-31G** and 6-311G(3d,2p) basis sets with and without diffuse functions were employed. A study of the topology of the charge density for the cyclic structures 2 and 3 was performed.