elements to which one needs access. What is the appeal behind the use of frozen-hydrated specimens for biological electron microscopy, and why is it so important that such a book should now have been written? If one cannot observe dynamic events as they are in progress, rapid specimen freezing at least offers the possibility to trap structures, organelles, macro­ molecules, or ions and other solutes in a form that is identical to what the native structure was like at the moment of trapping. The pursuit of this ideal becomes all the more necessary in electron microscopy because of the enormous increase in resolution that is available with electron-optical instruments, compared to light­ optical microscopes.