  We describe here how planetary ephemerides are built in the framework of
General Relativity and how they can be used to test alternative theories. We
focus on the definition of the reference frame (space and time) in which the
planetary ephemeris is described, the equations of motion that govern the
orbits of solar system bodies and {electromagnetic waves}. After a review on
the existing planetary and lunar ephemerides, we summarize the results obtained
considering full modifications of the ephemeris framework with direct
comparisons with the observations of planetary systems, with a specific
attention for the PPN formalism. We then discuss other formalisms such as
Einstein-dilaton theories, the massless graviton and MOND. The paper finally
concludes on some comments and recommendations regarding misinterpreted
measurements of the advance of perihelia.
