Scientific evidence clearly shows that chlorine and bromine compounds, such as CFCs, released into the atmosphere are responsible for continuous and progressive global ozone losses superimposed by dramatic seasonal ozone depletions first observed over Antarctica, now occurring over Arctic regions as well. Today substitutes are produced and emitted, some of which are highly reactive substances. This handbook volume deals with these reactive halogen compounds and their interactions. It provides a review on the present knowledge of their properties, applications, sources, sinks as well as international regulations.