Astrocytes functionally interact with neurons and with other brain cells. Although not electrically excitable, astrocytes display a complex repertoire of intracellular Ca signalling that evolves in space and time within single astrocytes and across astrocytic networks. Decoding the physiological meaning of these dynamic changes in astrocytic Ca activity has remained a major challenge. This Review describes experimental preparations and methods for recording and studying Ca activity in astrocytes, focusing on the analysis of Ca signalling events in single astrocytes and in astrocytic networks. The limitations of existing experimental approaches and ongoing technical and conceptual challenges in the interpretation of astrocytic Ca events and their spatio-temporal patterns are also discussed.