The present dissertation is essentially a collection of three investigations, in the context of the functional Renormalization Group. First, we will apply it to scalar models with internal O(N) symmetry, to study their universality classes and how the Mermin-Wagner theorem is seen in the RG framework. Next, we will use it to study Weyl-invariant systems, and in particular to obtain a nonperturbative proof that a quantization procedure respecting Weyl invariance is always possible, regardless of the field content of the theory. Finally, to investigate the corrections to the gravitational beta functions due to the anomalous dimensions of gravitons and ghosts.
