Astrocytes are the main class of neuroglia, serving a wide range of adaptive functions in the mammalian nervous system. They interact with neurons, providing structural, metabolic and trophic support for them. In pathological circumstances, astrocytes have the potential to induce neuronal dysfunction, but they can also play a neuroprotective role, releasing neuronal growth factors. Here we review recent findings regarding the role of astrocytes in the biology of the brain in physiological conditions, as well as their reaction following the onset of neurodegenerative disorders.