Temporal and spatial variations in the concentrations of signaling intermediates in a living cell are important for signaling in complex networks because they modulate the probabilities that signaling intermediates will interact with each other. We have studied 30 signaling sensors, ranging from receptors to transcription factors, in the physiological activation of murine ex vivo T cells by antigen-presenting cells. Spatiotemporal patterning of these molecules was highly diverse and varied with specific T cell receptors and T cell activation conditions. The diversity and variability observed suggest that spatiotemporal patterning controls signaling interactions during T cell activation in a physiologically important and discriminating manner. In support of this, the effective clustering of a group of ligand-engaged receptors and signaling intermediates in a joint pattern consistently correlated with efficient T cell activation at the level of the whole cell.