Astronomical transients are a hot topic in modern astrophysics, encompassing a broad range of phenomena. They can involve extreme physics, the most massive stars, neutron stars, black holes, explosions, mergers, or gravitational disruptions. They teach us about the limits of our Universe and are key to understanding the evolution of stars and galaxies, as well as the enrichment of the interstellar medium. The study of transientsis benefiting from the advent of new observational techniques, such as the use of gravitational waves, neutrinos, and cosmic particle showers. In the electromagnetic regime, observatories and instrumentation need to adapt to the specific requirements of rapid response and coordination. In this talk, I will review the different transient phenomena and their observational needs, how observing facilities have adapted to reach our current capabilities, and what prospects can be expected in the years to come. Progress in the study of astronomical transients is driven not only by optimised telescopes and instrumentation, but also by advances in observational techniques, data management, analysis tools, multi-observatory coordination, and the rapid and efficient communication of results