This teaching unit addresses the topic of seismic imaging at different scales through courses, a review of articles, and scientific questioning around data, numerical simulation, and Earth imaging. After a sequence of intensive courses on the numerical modeling of wave propagation by spectral element methods (10h), we will discuss through the critical reading of scientific articles, seismic imaging methods and their evolution for studying the Earth from near-surface layers to the core (10h). The assessment will be in the form of an oral presentation. Finally, mini-projects will consist of applying one or several of these techniques to study a chosen object, with a short report and an oral presentation (10 hours).