In this report we will discuss the possibilities to develop materials with performance considerably better than what is used today, commonly referred to as High Energy Density Materials (HEDM). The aim of this report, which is mostly based on the available literature, is to give an overview of the area, to see the possibilities of what could be achieved with different concepts, soon or in a longer time perspective. A historic review of energetic materials is given, followed by a short description of the computational tools needed to calculate the properties of new, not yet synthesized molecules and how to estimate the performance of new, conventional and exotic substances. These computational tools do not cover the concepts described in the area of exotic physics. After these introductory chapters follow chapters describing what HEDM´s could be synthesized using conventional chemistry, such as new fuel materials which includes nano materials, molecular composites and activated aluminium. In chapters on novel or exotic chemistry, all-nitrogen compounds, HEDM oxidizers, metastable states such as polymeric nitrogen, metallic hydrogen triplet helium and atomic propellants are described. The report ends with a chapter about more exotic ideas such as nuclear isomers and antimatter.