Book excerpt: This book provides a comprehensive analysis of the rules governing the taxation of permanent establishments as implemented in the OECD Model Tax Convention and German national tax law. Deviations between the OECD approach and the German approach are identified and modifications to the rules as a result of the Base Erosion and Profit Shifting (BEPS) project are examined. Moreover, challenges imposed to the PE concept as a result of the digitalisation of the economy are identified and discussed. Against this background, the Pillar One Blueprint proposing a long-term solution to overcome the tax challenges arising from the digitalisation of the economy is presented and assessed against widely accepted overarching principles of tax policy.