This book offers an in-depth analysis of the principle of proportionality in the EU insurance regulatory regime. It takes a critical look at how proportionality has been implemented in Solvency II and tests its effectiveness on captive (re)insurance undertakings. Given their unique business model, captives are considered the primary beneficiary of proportionality and therefore offer the perfect ‘litmus test’ for the principle’s effectiveness. In a world characterized by overregulation and increasingly complex financial markets, governments and policymakers face the challenge of regulating markets without hindering their growth. As ‘one-size-fits-all’ approaches have long-since been recognized as detrimental, the EU is seeking to develop a regulatory technique which allows more individual regulatory treatment while ensuring a level playing field. The first revolutionary step towards this goal was taken in Solvency II (Directive 2009/138/EC), which introduced a principle of proportionality to the EU insurance market. The principle is a unique tool which makes it possible to adjust the requirements of the Solvency II framework to the nature, scale, and complexity of each individual insurance undertaking’s risk profile. It is intended to help remove an unnecessary regulatory burden for insurance undertakings, and to prevent the proliferation of regulations in general. However, the practical implementation of proportionality is not without its share of obstacles. The principle’s generic nature and the lack of guidance have caused a great deal of confusion regarding its practical application and prevented insurance undertakings from using its benefits to the fullest. Consequently, the principle of proportionality has been subject to revision within the first Solvency II review process. The book will benefit captive owners, captive managers, regulators, supervisors, practitioners, academics, students and, more generally, all those involved with or interested in the insurance market.