The paper discusses the theoretical and phenomenological aspects of two-Higgs-doublet models (2HDMs) as extensions of the Standard Model. These models introduce scalar-mediated flavor-changing neutral currents (FCNCs), which are strongly constrained by experiments. Various strategies to control these FCNCs are explored, including natural flavor conservation scenarios such as Type I and Type II models, lepton-specific and inert models, and Type III models with tree-level FCNCs suppressed by Yukawa couplings or family symmetries. The phenomenology of charged scalars in these models is also analyzed. The role of symmetries in the scalar sector is examined, including six symmetry-constrained scalar potentials and their extension into the fermion sector. The vacuum structure of the scalar potential, including vacuum stability conditions and renormalization-group improvement, is studied. The stability of the tree-level minimum and its behavior under CP violation are discussed, with a detailed analysis of weak basis invariants and spontaneous CP violation. The paper also reviews recent results from the Large Hadron Collider (LHC) and concludes with a summary of key findings.The paper discusses the theoretical and phenomenological aspects of two-Higgs-doublet models (2HDMs) as extensions of the Standard Model. These models introduce scalar-mediated flavor-changing neutral currents (FCNCs), which are strongly constrained by experiments. Various strategies to control these FCNCs are explored, including natural flavor conservation scenarios such as Type I and Type II models, lepton-specific and inert models, and Type III models with tree-level FCNCs suppressed by Yukawa couplings or family symmetries. The phenomenology of charged scalars in these models is also analyzed. The role of symmetries in the scalar sector is examined, including six symmetry-constrained scalar potentials and their extension into the fermion sector. The vacuum structure of the scalar potential, including vacuum stability conditions and renormalization-group improvement, is studied. The stability of the tree-level minimum and its behavior under CP violation are discussed, with a detailed analysis of weak basis invariants and spontaneous CP violation. The paper also reviews recent results from the Large Hadron Collider (LHC) and concludes with a summary of key findings.