When animal rights activists enter farms or laboratories, they pose particular challenges for the law. How can the ethical motives of the activists be adequately taken into account in the legal assessment without giving them carte blanche for otherwise unlawful behaviour? This dissertation analyses, evaluates and compares the legislation and jurisprudence in Germany and other jurisdictions, particularly in the United States. In so doing, it incorporates the findings and methods of political theory alongside the legal assessment. The principles developed lay a foundation for a nuanced legal assessment of protest movements and methods on the limits of legality.