Public health has three core functions: assessment, policy development, and assurance. This framework, established by the Institute of Medicine in 1988 and adopted by the CDC, defines what every public health system should be doing to protect and improve the health of its community. Each function covers a distinct phase of the work, from identifying health problems to creating plans to solving them and making sure those plans actually work.
Assessment: Identifying Health Problems
Assessment is the intelligence-gathering arm of public health. It answers a straightforward question: what health problems exist in this community, and how serious are they? This function includes three main activities: assessing the health needs of a population, investigating health hazards and their effects, and analyzing what’s driving those health needs.
The primary tool here is surveillance, the ongoing, systematic collection and analysis of health data. Public health agencies track disease cases, hospitalizations, deaths, environmental exposures, and behavioral risk factors to build a picture of community health over time. This data collection serves different purposes depending on how it’s designed. Surveillance for tuberculosis, for instance, might focus on identifying people with active disease quickly enough to get them into treatment. Or it might track long-term trends to determine whether existing control measures are working. The objective shapes how frequently data is collected, how fast it needs to move through the system, and how complete it needs to be.
At the local level, assessment looks like a county health department tracking flu hospitalizations week by week, or investigating a cluster of lead poisoning cases in a neighborhood. At the state and federal levels, it looks like large-scale surveys on chronic disease prevalence, environmental monitoring, and national disease registries. Assessment also includes community health needs assessments, which are periodic, comprehensive reviews of a population’s health status, access to care, and social conditions. Without strong assessment, every other public health activity is essentially guesswork.
Policy Development: Setting Priorities and Plans
Once a community’s health problems are identified, policy development turns that information into action plans. This function involves three core activities: advocating for public health and identifying resources, setting priorities among competing health needs, and developing the plans and policies to address those priorities.
No community has unlimited resources, so prioritization is essential. If assessment reveals that a county has high rates of both diabetes and opioid overdose, policy development is where leaders weigh the severity, urgency, and feasibility of addressing each problem and decide how to allocate funding and staff. This process draws on the data collected during assessment but also requires input from community members, healthcare providers, elected officials, and other stakeholders.
Policy development isn’t limited to passing laws, though regulation is part of it. It includes strategic planning, writing grant proposals, building coalitions between organizations, drafting public health guidelines, and shaping the systems that deliver care. A local health department partnering with schools to create a childhood nutrition program is doing policy development. So is a state agency writing rules for restaurant food safety inspections. The common thread is translating evidence into organized, funded plans.
Assurance: Delivering and Evaluating Services
Assurance is where plans meet reality. This function ensures that the services and protections a community needs are actually available, accessible, and effective. It covers four activities: managing resources and organizational structures, implementing programs, evaluating those programs for quality, and informing and educating the public.
Some assurance activities are things a health department does directly, like running immunization clinics, conducting restaurant inspections, or providing prenatal care to underserved populations. Others involve making sure that someone in the community is providing necessary services, even if it’s not the health department itself. If a private hospital system is the main provider of mental health services in a region, the public health agency’s assurance role includes monitoring whether those services are reaching the people who need them.
Evaluation is a critical and often overlooked piece of assurance. Programs that aren’t measured can’t be improved. This means tracking outcomes (did childhood asthma rates decrease after an air quality initiative?), monitoring process measures (are enough people being screened?), and feeding results back into the assessment cycle so the whole system learns and adapts. Public health education, from antismoking campaigns to information about safe drinking water, also falls under assurance because it ensures that communities have the knowledge to protect their own health.
The 10 Essential Public Health Services
In 1994, these three core functions were expanded into a more detailed framework called the 10 Essential Public Health Services. This list spells out the specific activities that fall under assessment, policy development, and assurance, giving health departments a practical checklist for evaluating their own performance. The essential services range from monitoring health status and diagnosing health problems (assessment) to mobilizing community partnerships and developing policies (policy development) to enforcing laws, linking people to care, and ensuring a competent workforce (assurance).
The framework was significantly revised in 2020 to place equity at the center of all 10 services. The updated version explicitly calls on public health agencies to promote policies, systems, and community conditions that enable optimal health for all, and to actively remove systemic and structural barriers that have created health inequities. This was a meaningful shift. Rather than treating equity as one concern among many, the revised framework treats it as the foundation that every essential service should be built on.
How the Functions Work Together
The three core functions aren’t a linear process that starts at assessment and ends at assurance. They form a continuous cycle. Assessment identifies a problem. Policy development creates a response. Assurance implements and evaluates that response. The evaluation findings feed back into assessment, revealing whether the problem has improved, stayed the same, or shifted in unexpected ways. A new round of data collection refines the picture, priorities get adjusted, and programs evolve.
When any one function breaks down, the whole system suffers. Poor assessment means health departments don’t know what’s happening in their communities until a crisis forces attention. Weak policy development means good data sits unused, or resources go to lower-priority problems because of political pressure rather than evidence. Gaps in assurance mean well-designed programs never reach the people they were built for, or continue operating long after they’ve stopped being effective.
Every level of government shares responsibility for these functions. Local health departments typically handle the most direct, community-facing work: conducting inspections, running clinics, investigating disease outbreaks. State health departments coordinate across localities, manage statewide surveillance systems, and enforce public health law. Federal agencies like the CDC provide national surveillance data, fund state and local programs, set standards, and respond to threats that cross state lines. The framework is the same at every level, but the scale and scope of each function shifts depending on the agency’s jurisdiction.