Constituents often turn to members of Congress for assistance in securing changes to ZIP Code boundaries, usually because their mailing addresses do not correspond to the geographic and political boundaries of their municipalities' jurisdictions. This report explains why ZIP Code boundaries often are not aligned with geographic political jurisdiction boundaries, describes some problems that may occur because of the misalignment, and discusses efforts by the U.S. Postal Service (USPS) and Congress to address these problems. The Post Office Department (now the U.S. Postal Service) began dividing large cities into delivery zones in 1943, inserting two digits between the city and the state in the lower address line. In 1963, the whole country was divided into five-digit postal delivery codes—termed ZIP Codes by the Post Office. These codes corresponded to the post offices where final sorting of mail was done and from which letter carriers were dispatched to make deliveries. The term ZIP Code, originally trademarked and always capitalized, was an acronym for "Zoning Improvement Plan." Mass mailers were first required to use ZIP Codes in 1967, and today their use is ubiquitous. Almost all mail is sorted by machines, and the basis for this sorting is a ZIP Code. ZIP Codes have expanded through the years to 9 digits (ZIP+4) in 1983 and to 11 digits in 1991. Most customers know only their five-digit ZIP Codes. The first number in the ZIP Code represents a general geographic area of the nation—moving from a "0" for places in the east to a "9" for locations in the west. The second and third numbers indicate regions of the United States, while the fourth and fifth digits route the mail to specific post offices. For example, the ZIP Code for Alturas, the county seat of Modoc County in the northeastern corner of California, is 96101. The 9 directs the mail to the west. The 61 directs mail to the processing facility in Reno, NV, which is the distribution point for some California post offices such as Alturas, Cedarville (96104), Fort Bidwell (96112), and Likely (96116). Reno is also the processing facility for ZIP Codes in Nevada beginning with 894, 895, and 897. The four final ZIP Code numbers, which were added in 1983 "allow mail to be sorted to a specific group of streets or to a high-rise building." The Postal Service has contended that the ZIP Code system's only purpose is to facilitate the efficient and orderly delivery of the mail. Nevertheless, ZIP Code information is readily available to the public, and both private and governmental entities have found it a convenient and accessible tool for many purposes unrelated to mail delivery. Postal Service competitors like FedEx and UPS use the ZIP Code. The ZIP Code also has been adopted for non-delivery purposes, such as providing a convenient, yet sometimes imperfect means of targeting populations for performing demographic research, setting insurance rates, estimating housing values, remitting state tax revenues back to localities, and directing advertising messages. USPS works with state and local authorities as well as private companies to better align ZIP Codes with both postal and non-postal needs. Because ZIP Codes are based on the location of delivery post offices, they often do not correspond to political jurisdiction boundaries. This means that millions of Americans receive their mail from post offices in adjacent towns, villages, or neighborhoods. Their mailing addresses may not reflect the name and ZIP Code of the jurisdictions where they actually live. This situation was not uncommon when ZIP Codes were first assigned nearly 50 years ago, and it has become more common since then—particularly in rapidly growing suburban areas. The boundaries of many jurisdictions have changed with growth, annexation, and the incorporation of new communities. At the same time, USPS has sought to reduce rather than expand the number of post offices as its retail business model has changed. The widespread use of ZIP Codes for non-postal purposes has exacerbated problems for those postal patrons whose mailing addresses do not match their actual towns or cities of residence. The following is a sample of the problems that have been brought to congressional attention: higher automobile insurance rates for drivers who live in the suburbs but are charged city rates based on their ZIP Codes; residents who are confused about where to vote in municipal elections because they do not distinguish between their voting and mailing addresses; sales tax revenues rebated by states to the cities where they are collected often being misdirected because they are collected by merchants with ZIP Codes in different jurisdictions, or by merchants who mail their products to customers knowing only their ZIP Codes; individuals being sent jury duty notices when they are not eligible to serve based on their actual residences; emergency service vehicles being misdirected by confusion over what town a call has come from, based on mailing address information; and homeowners in expensive neighborhoods complaining that their housing values are diminished because their mailing addresses place them in less prestigious communities. In addition, a community may lack a delivery post office and complain that the need to use mailing addresses from neighboring towns robs them of their community identity. For example, even though Haddon Township, NJ, is an incorporated municipality with a 2009 estimated population of 14,368 people, it has no delivery post office, and its residents receive mail from the Camden, Haddonfield, Gloucester City, and Mount Ephraim post offices—each with a different ZIP Code. A host of ZIP Code misalignment problems were aired in a 1990 hearing of a House postal subcommittee. Ten members of Congress described ZIP Code alignment problems in their districts, and similar statements were received from many local governments, as well as the National League of Cities. The hearing in the 101 st Congress considered three bills ( H.R. 2380 , H.R. 2902 , and H.R. 4827 ) that would have allowed local governments, rather than the Postal Service, to determine local addresses or ZIP Code boundaries as a solution to the widespread problems. USPS expressed strong opposition to these bills and said that depriving USPS of control over "the most basic tool of the postal trade—the mailing address" would be "disastrous." A USPS boundary survey found that more than 11 million deliveries were served by carriers who cross municipal boundaries, and estimated that if delivery boundaries were realigned to match municipal boundaries, 1,600 new postal facilities and 10,500 new carriers would be needed. Also to be considered was the availability of additional ZIP Codes in certain large areas. At of the end of 1989, 924 of the 1,000 possible three-digit combinations already had been assigned; in 20 areas, 90 or more of the 100 possible ZIP Codes already had been assigned; and in Houston, all 100 possible ZIP Codes had been used. These arguments may have proved persuasive because the legislation never advanced, and neither have similar bills introduced in later Congresses. At the hearings, however, USPS also earned some criticism because of its "peremptory denials" of local suggestions or requests for ZIP Code changes that were variously characterized as "cold and haughty," "cursory," "unresponsive," "stonewalling," and "uncaring." The Government Accountability Office (GAO, then the General Accounting Office) examined postal case files on 26 municipal requests for ZIP Code changes, only 2 of which were approved by USPS. GAO reported that USPS not only could do a better job of providing facts and reasoning to explain its decisions in individual change requests, but also could "do more to ... resolve problems caused by conflicts between municipal and ZIP Code boundaries." In the years since the 1990 hearing and GAO's investigation, USPS has made a concerted effort to develop a process for the regular review of ZIP Code boundaries. Under Section 439 of the Postal Operations Manual , the manager of the District Office's Address Management System (AMS) is responsible for reviewing "and monitoring delivery growth patterns, facilities planning, and any other factors" that may affect ZIP Code boundaries. Increased growth in a geographic area is the most common precipitating factor in such USPS-initiated ZIP Code changes. USPS has established criteria and thresholds for ZIP Code changes, which include, but are not limited to, the establishment of 25,000 new deliveries or more than 55 carrier routes. ZIP Code changes are invariably sensitive locally, and often involve considerable coordination and investment, so USPS requires approval from the district manager, the manager of operations programs support, the manager of processing and distribution, and the district manager of customer service and sales before a proposal can be sent to the Area (regional) Office for approval. Most of the required ZIP Code change request analysis is based on operational considerations internal to USPS. One of the questions a manager of the District Office's AMS must address, however, is whether municipal boundaries will be crossed. The manager must also consider whether municipal officials have been asked to comment on the revised boundaries. The new boundary review process requires that "officials should consider municipal boundaries and customer interests in all zone splits. If a ZIP Code that is being considered for adjustment crosses municipal boundaries, consult municipal offices before submitting the proposal, and consider all reasonable solutions." The process for considering requests from municipalities and community groups for ZIP Code changes dates to March 1991—not long after the congressional hearing referenced above. It has taken some time for the process to become a settled practice, and for USPS to adopt a willingness to consider requests for boundary adjustments that are based solely on "community identity" concerns.