A tutorial review of diffraction tomography is given along with an overview of recent advances of this technique in borehole geophysics, ultrasonic imaging, and optical microscopy. First, the basic principles of diffraction tomography are presented. Then, we discuss a generalized inversion algorithm, valid for irregularly spaced data and a non-uniform background, and present reconstructions based on ultrasonic water tank data and underground georadar data. Next, we discuss a hybrid filtered backpropagation algorithm for ultrasonic and optical imaging. Quantitative images, based on experimental data, are presented of objects embedded in water or in biological tissue and probed by ultrasound, and of fibers embedded in an index matching liquid and probed by laser light.