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Neutrinos are the second most abundant particles in the Universe after photons, yet many of their properties remain poorly understood. In this talk, I will show how cosmological observations provide a powerful laboratory for probing neutrino physics beyond the Standard Model. I begin by discussing non-thermal light massive relics (LiMRs) which appear nearly indistinguishable at the linear level, this degeneracy is broken in the nonlinear regime. Using cosmological N-body simulations, we demonstrate that the formation of large-scale structure offers a robust way to distinguish between different production mechanisms. In particular, photometric galaxy surveys such as Dark Energy Survey, Euclid, and LSST have strong potential to constrain these scenarios. Next, I explore how non-standard neutrino interactions can address current cosmological tensions. In particular, neutrino-like particles interacting with a light scalar field in the early Universe can behave as an early dark energy component, offering a possible resolution to the Hubble tension. Finally, I discuss the so-called neutrino mass tension using a model-independent framework, highlighting how upcoming observations can further clarify the role of neutrinos in cosmology. |