  This paper is devoted to the study of the Reissner-Nordstr{\o}m-de Sitter
black holes and their maximal analytic extensions. In particular, we study some
of their properties that lays the groundwork for separate papers where we
obtain decay results and construct conformal scattering theories for test
fields on such spacetimes. Here, we find the necessary and sufficient
conditions on the parameters of the Reissner-Nordstr{\o}m-de Sitter metric
-namely, the mass, the charge, and the cosmological constant- to have three
horizons. Under this conditions, we prove that there is only one photon sphere
and we locate it. We then give a detailed construction of the maximal analytic
extension of the Reissner-Nordstr{\o}m-de Sitter manifold in the case of three
horizons.
