<p>In celestial mechanics, the computation of local quasi-integrals of the motion has been a central subject of study. Proper elements have been historically used for the classification of objects (like asteroids and Earth orbiters) as well as for the construction of local analytical solutions for the evolution of orbital elements. However, the domain where these quasi-integrals are well defined is naturally restricted by the existence of resonances. In this article, we use analytical methods to define quasi-integrals of motion in the case of resonant systems. This is done using the quasiperiodic properties of libration regions in isolated resonances, as well as in the multi-resonant case, allowing us to apply perturbation theory effectively even though the initial system was resonant. Finally, we introduce the problem of Earth orbiters, like satellites and space debris, and we illustrate the results of these methods in a variety of examples in mean motion and secular resonances, including thinner resonances and multi-resonant systems.</p>