X-ray diffraction phenomena have been used for decades to study matter at the nanometer and subnanometer scales. X-ray diffraction microscopy uses the far-field scattering of coherent X-rays to form the 2D or 3D image of a scattering object in a way that resembles crystallography. In this review, we describe the main principles, benefits, and limitations of diffraction microscopy. After sampling some of the milestones of this young technique and its close variants, we conclude with a short assessment of the current state of the field. Copyright © 2010 by Annual Reviews. All rights reserved.