The concept of a seismic image wave is introduced and explained with the aid of some examples. Seismic reflector images in various domains (e.g. depth-migrated reflections in the depth domain or common-offset reflections in the time domain) behave like snapshots of elementary body waves. These 'propagating' images are thus referred to as 'image waves'. The propagation variable, however, is now not time as it is for physical waves. It can be any other parameter involved in the seismic imaging process, for example the migration velocity or the common source-receiver offset. In parallel to the acoustic wave equation, which governs true elementary physical body waves, partial differential equations (here called the image-wave eikonal equation and the image-wave equation) can be derived that describe the propagation of image waves as a function of the problem-specific propagation variable. The concept of image waves is suited to solving a variety of different imaging problems. Image waves can be propagated, for example by a finite-difference or spectral-method algorithm.1252431442