The cover picture shows images and data from partially decomposed ammonium perchlorate (AP) particles. Ammonium perchlorate is the primary oxidizer used in high performance composite rocket propellant and is known for its excellent oxidizing properties. However, AP based propellants suffer from decomposition leading to extremely violent reactions during slow cook‐off events. The violence of this reaction is believed to be in part caused by the porosity developed within AP particles after heating for extended periods of time at temperatures below the orthorhombic to cubic phase transition temperature at 240°C. Moreover, from a fundamental scientific perspective, the partial decomposition of orthorhombic AP particles has shown peculiar features such as cessation of decomposition after losing approximately 30% of its mass, preferential decomposition based upon crystalline direction, and decomposition dependence on particle size including no decomposition for particles with diameters on the order of 3 micrometers. More details can be found in the Full Paper by Dr. Joseph Kalman et al. on page 1111.