Cover picture: Second-harmonic generation microscopy image of a primary cultured Aplysia neuron stained with the membrane dye DHPESBP. The signal is modulated by membrane potential and was found to be capable of recording action potentials with 0.6 µm and 0.833 msec spatiotemporal resolution. The high-resolution and deep tissue imaging capability of this nonlinear microscopy technique should prove valuable to future electrophysiology studies. For details, see the article by Dombeck et al. in this issue (pages 999–1003).