We give a brief summary of the formalism of invariants in generalscalar-tensor and multiscalar-tensor gravities without derivative couplings. Byrescaling of the metric and reparametrization of the scalar fields, the theorycan be presented in different conformal frames and parametrizations. Due tothis freedom in transformations, the scalar fields themselves do not carryindependent physical meaning (in a generic parametrization). However, there arefunctions of the scalar fields and their derivatives which remain invariantunder the transformations, providing a set of physical variables for thetheory. We indicate how to construct such invariants and show how theobservables like parametrized post-Newtonian parameters and characteristics ofFriedmann-Lemaitre-Robertson-Walker cosmology can be neatly expressed in termsof the invariants.
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