This chapter examines the increasing integration of cognitive and behavioral sciences, such as “behavioural insights” (BIs) and “nudging,” within the context of European public policies. It contextualizes this evolution by analyzing traditional market failures in public goods and the “complexities” that hinder policy effectiveness (agency effect, bounded rationality, systemic complexity). The philosophical debate between individual autonomy and paternalism is explored, demonstrating how behavioral economics has revealed human cognitive biases, challenging the neoclassical view of rationality, and promoting approaches such as “libertarian paternalism” and “nudging” (defined as a non-coercive “gentle push”). BIs are presented as a broader analytical approach, used upstream of policy formulation to inform the design of interventions, including coercive ones where justified by behavioral analysis. The chapter illustrates the concrete application of these methodologies by the European Commission, with examples ranging from consumer protection to financial services, culminating in a discussion of the establishment of dedicated BI units. In conclusion, it is argued that BIs and nudging offer an ethical-political “third way” to enhance the effectiveness of public policies, fostering “assisted individual autonomy” and a governance more attuned to citizens’ real decision-making dynamics.