Public policy is a course of action created and/or enacted, typically by a government, in response to public, real-world problems. 
One of the most known and controversial concepts of public policy is that of Thomas Dye, according to whom "public policy is whatever governments choose to do or not to do" (Dye, 1972: 2). 
Although widely used, Dye's concept is also criticized as being an empty concept. Dye himself admitted that his concept "discourages elaborate academic discussions of the definition of public policy - we say simply that public policy is whatever governments choose to do or not to do".
A theoretically grounded concept assumes public policy as "an institutionalized proposal to solve a central problem, guided by a conception". In some cases, this conception, which is the core of public policy, is a theory, when it is based on a logical explanation linking causes and consequences and able to be empirically tested. In this case, it's a theory of change or program theory.
The foundation of public policy is composed of national constitutional laws and regulations. Further foundational aspects include both judicial interpretations and regulations which are generally authorized by legislation. Public policy is considered strong when it solves problems efficiently and effectively, serves and supports governmental institutions and policies, and encourages active citizenship.
In his book 'Advanced Introduction to Public Policy', B. Guy Peters defines public policy as "the set of activities that governments engage in for the purpose of changing their economy and society", effectively saying that public policy is legislation brought in with the aim of benefiting or impacting the electorate in some way.  In another definition, author B. Dente in his book 'Understanding Policy Decisions' explains public policy as "a set of actions that affect the solution of a policy problem, i.e. a dissatisfaction regarding a certain need, demand or opportunity for public intervention. Its quality is measured by the capacity to create public value."
Other scholars define public policy as a system of "courses of action, regulatory measures, laws, and funding priorities concerning a given topic promulgated by a governmental entity or its representatives." Public policy is commonly embodied in "constitutions, legislative acts, and judicial decisions."
Public policy focuses on the decisions that create the outputs of a political system, such as transport policies, the management of a public health service, the administration of a system schooling and the organization of a defence force.
In the United States, this concept refers not only to the result of policies, but more broadly to the decision-making and analysis of governmental decisions. As an academic discipline, public policy is studied by professors and students at public policy schools of major universities throughout the country. The U.S. professional association of public policy practitioners, researchers, scholars, and students is the Association for Public Policy Analysis and Management.
Much of public policy is concerned with evaluating decision-making in governments and public bureaucracies.
Public policy making can be characterized as a dynamic, complex, and interactive system through which public problems are identified and resolved through the creation of new policy or reform of existing policy.
Public problems can originate in endless ways and require different policy responses (such as regulations, subsidies, import quotas, and laws) on the local, national, or international level. The public problems that influence public policy making can be of economic, social, or political nature. 
The Government holds a legal monopoly to initiate or threaten physical force to achieve its ends when necessary. For instance, in times of chaos when quick decision making is needed.
Public policy making is a time-consuming 'policy cycle'. The basic stages of policy cycle are as follows; a problem is identified, a policy response is formulated, the preferred solution is then selected and implemented, and finally the policy is evaluated. However, the evaluation stage takes an in-depth look into what can be learnt from the process as a whole, whether the original problem has been solved, and if not, what is recommended as an alternative course of action. Thus, returning policy makers to the first step, the identification.
Each system is influenced by different public problems and issues, and has different stakeholders; as such, each requires different public policy.
In public policy making, numerous individuals, corporations, non-profit organizations and interest groups compete and collaborate to influence policymakers to act in a particular way.
The large set of actors in the public policy process, such as politicians, civil servants, lobbyists, domain experts, and industry or sector representatives, use a variety of tactics and tools to advance their aims, including advocating their positions publicly, attempting to educate supporters and opponents, and mobilizing allies on a particular issue.
Many actors can be important in the public policy process, but government officials ultimately choose public policy in response to the public issue or problem at hand. In doing so, government officials are expected to meet public sector ethics and take the needs of all project stakeholders into account.
It is however worth noting that what public policy is put forward can be influenced by the political stance of the party in power. Following the 2008/2009 financial crisis, David Cameron's Conservative party looked to implement a policy of austerity in 2010 after winning the General Election that year, to shore up the economy and diminish the UK's national debt.  Whilst the Conservatives saw reducing the national debt as an absolute priority, the Labour Party, since the effects of Conservative austerity became apparent, have slated the policy for its 'needless' pressure on the working classes and those reliant on welfare, their 2019 election manifesto stating "Tory cuts [have] pushed our public services to breaking point" and that "the Conservatives have starved our education system of funding". This is a good example of how varying political beliefs can impact what is perceived as paramount for the electorate.
Since societies have changed in the past decades, the public policy making system changed too. In the 2010s, public policy making is increasingly goal-oriented, aiming for measurable results and goals, and decision-centric, focusing on decisions that must be taken immediately.
Furthermore, mass communications and technological changes such as the widespread availability of the Internet have caused the public policy system to become more complex and interconnected. The changes pose new challenges to the current public policy systems and pressures leaders to evolve to remain effective and efficient.
Public policies come from all governmental entities and at all levels: legislatures, courts, bureaucratic agencies, and executive offices at national, local and state levels. On the federal level, public policies are laws enacted by Congress, executive orders issued by the president, decisions handed down by the US Supreme Court, and regulations issued by bureaucratic agencies.
On the local, public policies include city ordinances, fire codes, and traffic regulations. They also take the form of written rules and regulations of city governmental departments: the police, fire departments, street repair, or building inspection. On the state level, public policies involve laws enacted by the state legislatures, decisions made by state courts, rules developed by state bureaucratic agencies, and decisions made by governors.
Data-driven policy is a policy designed by a government based on existing data, evidence, rational analysis and use of information technology to crystallize problems and highlight effective solutions. Data-driven policy making aims to make use of data and collaborate with citizens to co-create policy. Policy makers can now make use of new data sources and technological developments like Artificial Intelligence to gain new insights and make policy decisions which contribute to societal development.
User-centered policies are policies that are designed and implemented with the end-users, or those who are impacted by the policy, as co-designers. Policymakers using this design process utilize users' knowledge of their lived experiences.  This can allow for policymakers focus on including both comprehensiveness and comprehension within policies to aid in clarity for end-users, such as workers or organizations. 
The Small System dynamics model is a method of condensing and simplifying the understanding of complex issues related to overall productivity. 
Evidence-based policy is associated with Adrian Smith because in his 1996 presidential address to the Royal Statistical Society, Smith questioned the current process of policy making and urged for a more "evidence-based approach" commenting that it has "valuable lessons to offer".
Some policy scholars now avoid using the term evidence-based policy, using others such as evidence informed. This language shift allows continued thinking about the underlying desire to improve evidence use in terms of its rigor or quality, while avoiding some of the key limitations or reductionist ideas at times seen with the evidence-based language. Still, the language of evidence-based policy is widely used and, as such, can be interpreted to reflect a desire for evidence to be used well or appropriately in one way or another - such as by ensuring systematic consideration of rigorous and high quality policy relevant evidence, or by avoiding biased and erroneous applications of evidence for political ends.
Unlike the UK, the USA has a largely devolved government, with power at local, state and federal level. Due to these various levels of governance, it can often be difficult to coordinate passing bills and legislation, and there is often disagreement. Despite this, the system allows citizens to be relatively involved in inputting legislation. Furthermore, each level of government is set up in a similar way with similar rules, and all pump money into creating what is hoped to be effective legislation. Policy creation in America is often seen as unique to other countries.
As an academic discipline, public policy brings in elements of many social science fields and concepts, including economics, sociology, political economy, social policy, program evaluation, policy analysis, and public management, all as applied to problems of governmental administration, management, and operations. At the same time, the study of public policy is distinct from political science or economics, in its focus on the application of theory to practice. While the majority of public policy degrees are master's and doctoral degrees, there are several universities that offer undergraduate education in public policy. Notable institutions includes:
Traditionally, the academic field of public policy focused on domestic policy. However, the wave of economic globalization that occurred in the late 20th and early 21st centuries created a need for a subset of public policy that focused on global governance, especially as it relates to issues that transcend national borders such as climate change, terrorism, nuclear proliferation, and economic development. Consequently, many traditional public policy schools had to adjust their curricula to better suit this new policy landscape, as well as develop entirely new curricula altogether.