The specialist book "Between Form and Formality" by Paul Eichmüller offers an in-depth analysis of the criteria for distinguishing the effectiveness of contracts according to Article 11 of the Rome I Regulation. It highlights the challenges arising from the distinction between substantive prerequisites and formal requirements. In particular, it examines how Austrian contract law classifies various norms as "formality," while their classification in the context of European private international law (PIL) often remains unclear. The work addresses specific examples such as the notarization requirement for GmbH share purchases and the written form requirements for contracts with minors. By defining relevant criteria for delineating the European form statute, the book makes a valuable contribution to the legal discussion and provides practical insights for legal professionals and students in the field of civil law.