The discovery of high-energy cosmic neutrinos has opened a new frontier in astroparticle physics, providing a unique window into the most extreme environments in the universe. Identifying their sources is not only key to understanding neutrino origins, but also central to solving the century-old mystery of cosmic-ray origins and their acceleration mechanisms. In this talk, I will discuss the theoretical implications of the latest observations and highlight the growing impact of multimessenger approaches in this field. I will present recent developments on high-energy neutrino emission from extragalactic gamma-ray–dark sources and from regions near the Galactic plane. If time permits, I will also explore the potential of high-energy neutrinos as probes of physics beyond the Standard Model.