In this chapter, the steps are discussed of how to obtain a seismic reflectivity image from seismic records. Here, we assume that the records only contain reflections. Before we discuss these steps, we derive which property gives a reflection back form a boundary: the impedance contrast, also called the reflectivity. Then we will discuss the main basic steps of a processing sequence, commonly used to obtain a seismic image and common to seismic data gathered on land (on-shore) as well as at sea (off-shore): CMP sorting, velocity analysis and NMO correction, stacking, (zero-offset) migration and time-to-depth conversion.