This report is part of the FOI delivery to FMV and the Armed Forces concerning the acquisition of a new ballistic helmet. The purpose of the FOI study of ballistic helmets has been to support FMV with background information for criteria and test methods on factors related to physical protection. A literature review for research on the physical protection of ballistic helmets in international conferences and databases were performed. Included in the analysis was also information from the Canadian DRDC on their helmet project AMMPHS. Out of the 89 surveyed articles, 20 focused on ballistic protection. The main developments in the ballistic protection were the hybridization of existing fibres and new helmet manufacturing techniques. 25 papers on Behind Helmet Blunt Trauma were found that mostly concerned testing methods using head surrogates. In particular, DRDC and Biokinetics had been publishing a number of papers on their test rig "The Biokinetics Head Form". Another trend in helmet development has been to increase the protection against blunt trauma in the infantry helmet. The papers focused mainly on testing but also development of new more energy-absorbing materials for use as liner material. Blast seemed to have increased in interest due to the increased frequency of concussions (mTBI) in statistical data. The word "blast" is often used for explosive events and may include not only high pressure but also secondary injury mechanisms like accelerations and blunt impacts to the head. Supplementary protection like mandible guards and visors, covered area and ergonomics were other areas of interest that have been studied in the literature. Statistical data from contemporary conflicts has been used to study the frequency of injuries in different body regions which in turn can be linked to the analysis of body armour design. Areas that need further study is the maximum allowable head borne mass, minimum requirements for ballistic protection, measurement of BHBT, level of shock-absorbing protection, and the need for additional protection and increased covered area.