This book deals with a similar revolution (albeit on a different time scale) in the study of the cell’s ultrastructure, brought about by the application of tomographic techniques to electron microscopy. For a long time, structural information about cell components had to be inferred from images of thin sections, the thickness being limited by the path length of 100-kV electrons in biological matter. The limitations of sectioning are well known: it produces distortions and material loss, and additional errors arise in the attempt to stack the section images to form a three-dimensional representation. Organelles of complex shape have proved difficult or impossible to study in this way. The problem is solved by increasing the voltage to the range of 400 to 1000 kV, thereby increasing the penetration thickness, and using a series of views rather than a single one to generate a ‘true’ threedimensional image. Again, an inside look is obtained into the structure, which remains intact during the investigation.