Initially, this chapter undertakes a critical analysis and discussion on the connotations and evolutionary development of concepts pertinent to energy policy and its instruments. It delineates several distinct characteristics of energy policy, including its highly interventionist nature, comprehensive coordination, long-term and strategic dimensions, geopolitical traits, systemic and holistic aspects, dynamism, flexibility and adaptability, and regional variability. Furthermore, the classification of energy policies is elaborated from multiple perspectives, including the varying issuing entities, scopes of implementation, policy objectives, implementation tools, and target groups, encompassing both domestic and international viewpoints. The chapter emphasizes the formulation of diverse, targeted, complementary, and dynamic policy instruments tailored to different policy objectives and types of energy, noting that preferences and institutional frameworks vary by country, thus influencing the selection of policy tools. Subsequently, foundational theories from various disciplines such as political science, economics, sociology, environmental science, international relations, and technological innovation that are pertinent to the study of energy policy are expounded. Lastly, a comprehensive review of both the cutting-edge issues and methodologies in energy policy research is presented.