Analogously to chlorine, bromine has been shown to have a role in high temperature corrosion and dioxin/furan formation in combustion systems. This paper presents a review on the origin, content and modes of occurrence of bromine in solid substances used as fuels. In Part 1 the natural and in Part 2 the anthropogenic occurrence of bromine is discussed. The reader is provided with a comprehensive background to understand the factors influencing bromine sources and content in fuels as well as the implications of bromine on combustion systems. Bromine has both natural and anthropogenic sources depending upon the fuel type, the most important of which are the deposition of sea salts and the utilisation of brominated flame retardants (BFRs), respectively. Nor can the influence of various brominated chemicals such as biocides be disregarded. Bromine content exhibits large variation in fuels. The BFR treated plastics can contain several weight percentages of bromine whereas up to 500 mg kg(-1) has been found in municipal solid waste (MSW) and Solid Recovered Fuel (SRF). Industrial and residential water treatment (sanitising, slime control) may involve the use of brominated biocides which results in bromine residuals in sludge -up to approximately 100 mg kg(-1). Bromine is applied in other selected uses such as colourants, rubber additives and in photographic paper which may be found in solid waste fuels, too. (C) 2011 Elsevier Ltd. All rights reserved.