In the past 20 years, glial cells have been elevated from being considered as passive elements during neuronal transmission. By eliciting astroglial calcium rises, so-called gliotransmitters such as glutamate, ATP, or D-serine can be released and the activity of neighboring neurons modulated. However, this emerging picture has been challenged. Agulhon et al. (see the Perspective by Kirchhoff) reexamined these questions using two previously characterized mouse models. Calcium elevations induced selectively in astrocytes caused no change in multiple measures of synaptic activity. Furthermore, in mutant mice unable to elevate intracellular calcium, all synaptic measures were at wild-type levels. Astrocytic calcium signaling activity was thus not tied to the release of gliotransmitters and did not affect synaptic transmission or short- and long-term synaptic plasticity.