This lecture covers the principles and applications of X-ray tomography, including X-ray Computed Tomography (XCT) and X-ray microtomography (XTM). It explains the experimental setup at synchrotrons, the differences between XCT and XTM, and the constraints and resolutions of each technique. The presentation also discusses the use of synchrotron radiation in XTM and showcases various examples of tomographic images in medical and scientific fields.