The ASTRA Tomography Toolbox is a MATLAB toolbox based on high-performance GPU primitives for 2D and 3D tomography, developed jointly by the ASTRA-Vision Lab research group at the University of Antwerp and CWI, Amsterdam. It supports 2D parallel and fan beam geometries, and 3D parallel and cone beam. All of them have highly flexible source/detector positioning. A large number of 2D and 3D algorithms are available, including FBP, SIRT, SART, CGLS. The basic forward and backward projection operations are GPU-accelerated, and directly callable from MATLAB to enable building new algorithms.