Geospatial data abstraction library (GDAL) is a free library dedicated to the reading and writing of geospatial data in both raster and vector format. GDAL runs on all modern operating systems (Unix-like OS, Windows). Quantum geographic information system (QGIS) also provides access to most GDAL utility programs, giving users the ability to process, analyze and modify raster files namely: satellite images, aerial photographs, and digital terrain models. These tools can be called in two ways, either with the GdalTools extension, integrated by default in the QGIS Raster menu, or with the Processing Toolbox. This chapter presents the main GDAL tools available in QGIS, in particular in the GdalTools extension. It describes the data used in the practical examples and focuses on reading and describing the metadata. The chapter deals with basic utilities for processing an image. It explains some algorithms dedicated to raster analysis, focusing in particular on the derivatives computed from an elevation model.