An actuary is a professional with advanced mathematical skills who deals with the measurement and management of risk and uncertainty. These risks can affect both sides of the balance sheet and require asset management, liability management, and valuation skills. Actuaries provide assessments of financial security systems, with a focus on their complexity, their mathematics, and their mechanisms. The name of the corresponding academic discipline is actuarial science.

While the concept of insurance dates to antiquity, the concepts needed to scientifically measure and mitigate risks have their origins in 17th-century studies of probability and annuities. Actuaries in the 21st century require analytical skills, business knowledge, and an understanding of human behavior and information systems; actuaries use this knowledge to design programs that manage risk, by determining if the implementation of strategies proposed for mitigating potential risks does not exceed the expected cost of those risks actualized. The steps needed to become an actuary, including education and licensing, are specific to a given country, with various additional requirements applied by regional administrative units; however, almost all processes impart universal principles of risk assessment, statistical analysis, and risk mitigation, involving rigorously structured training and examination schedules, taking many years to complete.

The profession has consistently been ranked as one of the most desirable. In various studies in the United States, being an actuary has been ranked first or second multiple times since 2010.

Actuaries use skills primarily in mathematics—particularly calculus-based probability and mathematical statistics—but also economics, computer science, finance, and business. For this reason, actuaries are essential to several sectors:

Actuaries assemble and analyze data to estimate the probability and likely cost of an event such as death, sickness, injury, disability, or property loss. Actuaries also answer financial questions: these questions include the level of pension contributions needed to produce a certain retirement income, and how a company should invest resources to maximize the return on investment in light of potential risk. Using broad knowledge, actuaries help to design and price insurance policies, pension plans, and other financial strategies so as to ensure that the plans are maintained on a sound financial basis.

Most traditional actuarial disciplines fall into two main categories: life and non-life.

Life actuaries, who include health and pension actuaries, primarily deal with three kinds of risk: mortality, morbidity, and investment. Products prominent in their work include life insurance, annuities, pensions, short and long term disability insurance, health insurance, health savings accounts, and long-term care insurance. In addition to actuarial risks, social insurance programs are influenced by public opinion, politics, budget constraints, changing demographics, and other factors such as medical technology, inflation, and cost of living considerations.

Non-life actuaries, also known as "property and casualty" (mainly US) or "general insurance" (mainly UK) actuaries, deal with both physical and legal risks that affect people or their property. Products prominent in their work include auto insurance, homeowners insurance, commercial property insurance, workers' compensation, malpractice insurance, product liability insurance, marine insurance, terrorism insurance, and other types of liability insurance.