Photoelectron holography produces three dimensional images of surface sites with atomic scale (0.5Å) resolution. While experimentally identical to two angle photoelectron diffraction, photoelectron holography is a true holographic technique. The atomic resolution images can be obtained by Fourier transformation. I will review the principles of holography, focusing on the orginal work of the inventor of holography, D. Gabor, and the principles of photoelectron diffraction, discussing my own view of the important steps which brought us to our present understanding. Finally I will show how photoelectron holography partially fulfills the orginal goals of Gabor and provides the long sought direct-analysis of photoelectron diffraction for surface structure determination. © 1990.