In this presentation, I will discuss lepton and baryon number violation using an Effective Field Theory (EFT) approach. In particular, in the first part of the talk, I will analyse the generation of tree-level Majorana neutrino masses by the introduction of new scalar multiplets at the electroweak scale, which acquire vacuum expectation values (VEVs). We will elucidate the underlying UV completions for these effective operators, specifically the new seesaw models, and investigate their impact on neutrino masses, including contributions at the loop level. We will discuss the phenomenology of these scenarios, including constraints from Electroweak Precision Tests, Lepton Flavor Violation, and colliders. In the second part of the talk, I will explore nucleon decays using SMEFT operators up to dimension 9. We will present estimates for the rates of various nucleon decay channels and use these to extract model-independent lower limits on the energy scale associated with these processes. Additionally, we will investigate potential correlations among processes.