Abstract: With just the Standard Model Higgs doublet, there are only three types of seesaw models that generate light Majorana neutrino masses at tree level after electroweak spontaneous symmetry breaking. However, if there exist additional TeV scalars acquiring vacuum expectation values, coupled with heavier fermionic multiplets, several new seesaw models become possible. In this talk, I will discuss scenarios with one or two new scalars up to quintuplet SU(2) representations and their tree-level UV completions. In addition to the tree-level generation of neutrino masses, we also consider the one-loop contributions and construct low-energy versions that exhibit a very rich phenomenology. I'll present the constraints on the scalar sector from direct searches at colliders, loop corrections to electroweak precision tests as well as scrutinize the generation of dimension-6 operators and explore their implications, including non-unitarity of the leptonic mixing matrix, non-universal Z−boson interactions, and lepton flavor violation.