A typical electron diffraction pattern recorded from an untilted AQP0 2-D crystal prepared by the carbon sandwich technique (Gyobu et al., 2004), showing diffraction spots to a resolution beyond 2 Å. [Reproduced with permission from Fig. 1(b) of Gonen et al. (2005), Nature (London), 438, 633–638.] The specimen is cooled by liquid helium.