Cover picture: Emission ratio (535/480 nm) imaging of calcium waves in HeLa cells expressing yellow cameleon-2.1 recorded with a video-rate scanning, two-photon excitation system. A calcium wave (pseudocolor red), elicited by 0.1 mM histamine, can be seen to propagate across each cell. Reading from left to right and then down, the first image was recorded 1 s before histamine; the next four were taken after histamine and spaced 133 ms apart. The last image was 6 s after histamine. See the article by Fan et al. on p. 2412.