This paper investigates traditional and new tools for increasing the effectiveness of rules and enforcement strategies. As a preliminary concern, it underlines that there are two sides to effectiveness that cannot be approached separately: effectiveness as perfect compliance with the terms of rules, and effectiveness as a result of rules which incentivise behaviours to meet the “spirit of the law”. In order to achieve this comprehensive approach to effectiveness, rules must be evidence-based, plain, understandable and accepted. Moreover, a clear understanding of compliance drivers is needed. Deterrence and all other possible motivations that go beyond the rational calculus should be assessed by decision-makers, such as internal motivation, procedural fairness, cooperation, social norms, heuristics and bias. Enriching the rationality assumption with other drivers of compliance does not mean dismissing traditional rules or enforcement tools, which conversely remain crucial for the purpose of supporting voluntary compliance and for preventing non-compliance. However, deterrence should be calibrated by a risk-based, responsive and proportional approach to (simplified) rules and enforcement strategies. Trust in public authorities, supportive and cooperative public administrations are also fundamental in order to increase voluntary compliance, and a cognitive-based approach should complement these views.