Whether astrocytes are able to regulate neurotransmission and local blood flow over short (millisecond) timescales is unclear. Here, genetically encoded calcium indicators and simultaneous two-photon imaging were used to monitor spatiotemporal calcium dynamics within fine astrocyte processes and endfeet in layer II/III whisker barrel cortex of awake mice. During spontaneous activity and neuronal activity evoked by whisker stimulation, astrocytes showed fast calcium signals that rapidly followed nearby neuronal activity, suggesting that astrocyte signals are fast enough to contribute to synaptic modulation and neurovascular coupling.