In the era of multi-messenger astronomy, ultra-high-energy cosmic rays (UHECRs) offer a unique window into the nature of astrophysical sources and particle interactions at energies far beyond the reach of current particle accelerators. This talk will present selected recent results, focusing on the energy spectrum, nuclear mass composition and anisotropies, highlighting how these observations can constrain astrophysical scenarios involving both steady and transient sources. Additionally, the study of secondary emissions, produced both at the source and during propagation through extragalactic space, offers critical complementary insights within the multi-messenger context.