I briefly present the baselines of Quantum Field Theory in Curved Spacetimes (QFTCS), which investigates the consequences of defining a quantum field theory for the matter and its interactions in a curved spacetime background described by General Relativity. Although being an effective theory, QFTCS
allows the prediction of quantum gravity effects, like thermal evaporation of black holes, known as the Hawking effect. Using the framework of QFTCS, one can also reexamine relevant conceptual issues in Physics such as particle production (e. g. in an expanding universe), equivalence principle,
etc. Indeed, after the first developments in QFTCS, the particle concept itself has been revisited, from the point of view of different observers, leading to the Unruh effect, which states that the Minkowski vacuum,
identified with the absence of real particles according to inertial observers, manifests itself as a thermal bath of real (Rindler) particles to uniformly accelerated observers. In this context, we analyze the radiation
emitted by accelerated sources from the point of view of co-accelerated observers and examples of how the presence of boundaries may influence radiation emission processes. QFTCS allows also to obtain corrections due to spacetime curvature in quantum phenomena occurring near black holes and
relativistic stars. As particular examples, we comment on radiation emission processes of sources and charges rotating around black holes, and exhibit results obtained for absorption and scattering cross sections for Schwarzschild and Reissner-Nordström black holes, as well as for acoustic analogues of black holes.