A public utility is an entity that provides the general public with essential goods and services such as electricity, natural gas, energy, water, sewer, heat, telecommunications (telephone, fiber optic or broadband internet), railroad, and rail transit.

Public utilities (goods and services) are often provided by a public utility corporation that is essentially given a monopoly over the provision of the good or service in a certain geographic area—and exemption from antitrust and unfair competition laws—in exchange for certain governmental restrictions and regulations. Public utility companies are often regulated by a governmental Public Utility Commission (PUC).

The laws and rules that govern public utilities are usually located in state or federal statutes—depending on whether the utility is regulated by the state or federal government. For example, many states have a public utilities code—sometimes called a public utility regulatory act—or provide for public utility corporations and their regulation in the state administrative code. The Federal Energy Regulatory Commission (FERC) is one example of a PUC at the federal level.

In Massachusetts, public utilities such as electricity, natural gas, water, and telecommunications are regulated by the Massachusetts Department of Public Utilities (DPU). The DPU oversees these utilities to ensure that they provide safe, reliable, and cost-effective service to consumers while allowing for reasonable rates of return for the utility companies. Public utilities in Massachusetts are typically granted a monopoly in a specific geographic area, but in return, they are subject to regulation regarding their rates, operations, and service standards. The DPU also ensures that public utility companies adhere to environmental standards and public safety requirements. At the federal level, agencies like the Federal Energy Regulatory Commission (FERC) regulate aspects of utility services that cross state lines, such as the transmission and wholesale sale of electricity and natural gas. The interplay between state and federal regulation ensures that public utilities operate within a framework designed to protect consumers and maintain service quality, while also promoting infrastructure investment and energy conservation.