Sometimes the answers to questions are not straightforward; one has to trace the way backward to find the answers. Framing an exact question for a given answer is even more difficult than finding an answer to a question. Typical inverse problems arise from asking simple questions 'backward'. Most problems given in mathematics classes are forward problems, with well-defined answers. Yet, most real-life problems are inverse problems. We don’t know the actual equations of the world, and even if we did, our measurement of reality would have uncertainty. Read the learning module to explore the real-time applications of inverse problems such as X-rays, remote sensing, and environment modeling.