班号共用（英语：Code-sharing），又称「共挂班号」、「联营航班」，，是现代航空业其中一种相当普遍的经营模式，由多家航空公司共同经营某一航线，常见于以接驳长途航班的短途航班上，也偶见于以商务旅客为主、班次频密的短途航班。简单来说，就是航空公司之间的“买位”制度，让未有飞行该航线的航空公司，能通过购入其他航空公司航班的机票再出售予顾客。班号共用的协议是建基于过往联程机票的制度上，并进一步发展成全球性的航空公司联盟。目前国际上三大航空公司联盟——星空联盟、天合联盟及寰宇一家，最初都是由原本就有班号共用合作的航空公司组成联盟的核心集团，再逐渐吸收新伙伴而扩大成今日的规模。

A codeshare agreement, sometimes simply codeshare, is an aviation business arrangement where two or more airlines share the same flight. Sharing, in this sense, means that each airline publishes and markets the flight under its own airline designator and flight number as part of its published timetable or schedule. A seat can be purchased on each airline's designator and flight number, but is operated by only one of these cooperating airlines, commonly called the operating carrier or more precisely (and in line with definitions in IATA Standard Schedules Information Manual): "Administrating carrier". The term "code" refers to the identifier used in flight schedule, generally the two-character IATA airline designator code and flight number. Thus, XX123 (flight number 123 operated by the airline XX), might also be sold by airline YY as YY456 and by ZZ as ZZ9876. Airlines YY and ZZ are in this case called "Marketing airlines" (sometimes abbreviated MKT CXR for "marketing carrier"). Most of the major airlines today have code sharing partnerships with other airlines, and code sharing is a key feature of the major airline alliances. Typically, code-sharing agreements are also a part of the commercial agreements between airlines in the same airline alliances.