The powers and duties of first class cities, second class cities and towns are set forth in Title 35 of the Revised Code of Washington. The powers and duties of optional municipal code cities are set forth in Title 35A of the Revised Code of Washington.

Currently there are 10 first class cities, 11 second class cities, 72 towns, and 187 code cities. Waitsburg is the only unclassified city and operates under a territorial charter.

There are four classes of municipal government in Washington: first and second class cities, towns and the optional municipal code classification. Cities and towns are classified according to their population at the time of incorporation or reorganization. First class cities have populations over 10,000; second class cities have populations over 1,500, and towns have populations less that 1,500. An additional classification, known as the optional municipal code, was devised in 1967 as an alternative to the existing classification system and provides cities that adopt the code with broad statutory home rule authority. The optional municipal code classification is available to any city or town without regard to population. While all cities and towns possess the same basic authority to perform general governmental functions, there are several important differences depending both upon the size of the city and its classification. For example, the laws that regulate purchasing by cities and towns and which require competitive bidding, establish different requirements depending upon a city's population and classification.

The 1994 legislature made some significant changes to the state laws governing incorporations. As a result of these changes the minimum population now required to incorporate as a city is 1,500. Since a new city cannot be formed unless it has at least 1,500 inhabitants, incorporation as a town is no longer an option (i.e., new cities must incorporate as either first or second class cities, or as optional municipal code cities).