We discuss some of the signatures associated with extensions of the Standard Model related to the neutrino and electroweak symmetry breaking sectors, with and without supersymmetry. The topics include a basic discussion of the theory of neutrino mass and the corresponding extensions of the Standard Model that incorporate massive neutrinos; an overview of the present observational status of neutrino mass searches, with emphasis on solar neutrinos, as well as the cosmological data on the amplitude of primordial density fluctuations; the implications of neutrino mass in cosmological nucleosynthesis, non‐accelerator, as well as in high energy particle collider experiments. Turning to the electroweak breaking sector, we discuss the physics potential for Higgs boson searches at LEP200, including Majoron extensions of the Standard Model, and the physics of invisibly decaying Higgs bosons. We discuss the minimal supersymmetric Standard Model phenomenology, as well as some of the laboratory signatures that would be associated to models with R parity violation, especially in Z and scalar boson decays. ©1996 American Institute of Physics.