Public policy is a foundational mechanism through which governments address societal challenges, allocate resources, and pursue collective goals. This review critically synthesizes contemporary theoretical and empirical literature (2018–2025) on three interconnected stages of the policy process: formulation, implementation, and assessment. Unlike prior reviews that treat these stages separately or draw predominantly on health and environmental policy, this review integrates all three stages within a single conceptual framework linking contextual factors, actor behavior, and feedback mechanisms to policy outcomes, and it extends the evidentiary base to education, social welfare, and digital governance. We compare major theoretical frameworks, including the multiple streams model, advocacy coalition framework, punctuated equilibrium theory, street-level bureaucracy theory, and the Consolidated Framework for Implementation Research, not merely by describing them but by critically appraising their respective strengths, limitations, and contextual applicability. Policy formulation involves agenda setting, problem definition, and the structured design of interventions, increasingly shaped by stakeholder participation and evidence integration. Implementation translates policy intent into action through top-down, bottom-up, and hybrid governance mechanisms, with organizational capacity, bureaucratic discretion, and intergovernmental coordination playing decisive roles across sectors. Assessment encompasses process, outcome, impact, and economic evaluation methods that determine whether policies achieve intended effects, generate unintended consequences, or require redesign. We give particular attention to equity, moving beyond a general call for inclusion to describe practical indicators and tools including equity-focused impact assessments and disaggregated outcome monitoring, that can be embedded at each stage of the cycle. Tables and figures synthesize comparative data on evaluation frameworks, implementation determinants, and outcome metrics, alongside a new integrative conceptual model linking formulation, implementation, assessment, feedback loops, and contextual moderators. This review concludes by identifying specific priorities for future research, including artificial intelligence and real-time policy analytics, adaptive governance architectures, and policy evaluation capacity in low- and middle-income countries.