Mechanistic insight into the biochemistry of carbon-halogen bond cleavage is rapidly growing because of recent structural, biochemical and computational studies that have provided further insight into how haloalkane dehalogenases achieve their impressive catalytic activity. An occluded water-free active-site cavity together with strong hydrogen bond donating groups reduce the transition state energy barrier compared with that of the non-enzymatic reaction in water. Even though all known haloalkane dehalogenases belong to the alpha/beta-hydrolase fold family, there are interesting differences in mechanistic and kinetic details, as shown by properties of mutant enzymes and transient-state kinetic studies. To improve enzymatic degradation of some environmentally important recalcitrant compounds, site-directed mutagenesis and directed-evolution studies are being done.