The broad topic of decontamination science is a high priority to most of the partner departments and organisations of the Centre for Security Science. The scope of project CSSP-2013-TI-1036 is to address selected areas of decontamination science and capabilities. The subject of this document is identification of the knowledge gaps surrounding decontamination and chemical-biological-radiological-nuclear personal protective equipment (CBRN PPE), including decontamination of PPE appropriate to the activities performed by emergency responders and selection of PPE for the decontamination line. In order to identify these knowledge gaps, current best practices for decontamination that are employed by different user groups or agencies are reviewed, along with a review of scientific literature and research to support or validate those practices, particularly in the area of selection and decontamination/doffing of PPE. The status of knowledge has been summarized in the general topic areas such as protection and procedures for decontamination for the various types of event (chemical, biological, radiological); use in extreme climate (hot or cold); hospital decontamination; and performance requirements for, and logistics of, re-use or PPE designed for more than CBRN response. The most important specific areas that would benefit from immediate effort would be: enhancement of our knowledge of performance, technology, and requirements for managing personnel decontamination in extreme temperature; determination and detection of allowable residual contamination on skin; concepts for re-use and multi-purpose CBRN PPE; and finally, transition of all of this information to guidance documents and standards.