The internationalisation and performance relation is subject to a controversial discussion: rationales and empirical results range from a linear positive or negative link to different curvilinear models - a conflict resolved in this paper. First, this book offers a comprehensive review of international business theory and past research. Moreover, concepts for operationalising internationalisation are thoroughly evaluated and improved with respect to measuring different dimensions of foreign business: the depth of international operations, cultural distance and international organisational structure. Finally, the considerable lack of systematic insights into the core components of firms' efficiency is tackled. By analysing 6 efficiency ratios on Germany's top 100 manufacturers over a 7 year period and linking these to overall profitability, the interplay of different facets of foreign involvement and performance becomes visible for the first time in international management literature.