From 1995 on all new vehicles sold in Germany must be fitted with an electronic immobilizer. This measure was part of a comprehensive police plan which, adopted in 1994, reacted to the unprecedented increase in vehicle theft after German re-unification and the breakdown of the former USSR. While international research has already shown that electronic immobilization is an effective tool to reduce vehicle thefts, comparable studies for Germany have not existed. Based on the situational crime prevention approach, this study indicates that the substantial vehicle theft reductions recorded over the last 15 years in Germany can be explained in particular by the introduction of electronic immobilizers as a 'target hardening' mechanism. It will be shown that immobilizers not only effectively obstruct opportunistic vehicle thieves, but also increase the efforts of professional vehicle trafficking groups. Since an external impact evaluation has never been planned for this measure, the study followed a mixed methods approach in using available police data as well as complementary interviews with key experts. (Published Abstract)