Code-sharing agreements are widely used in the aviation industry. In the aviation industry, the term code refers to the double-digit XX used as a prefix in flight numbers. For example, flight nr. UA123 a United Airlines flight. The UA code helps identify the airline involved. These codes are given by IATA, an international travel and tourism organization. There are different types of codeshare agreements: most major airlines today have codeshare partnerships with other airlines, and code sharing is an essential feature of major airline alliances. In general, code-sharing agreements are also part of trade agreements between airlines in the same alliances. This type of code sharing is widespread in the United States and is also known as capacity purchase. In doing so, the operating company sells seats on its aircraft for the sole benefit of marketing. There are different forms of this type of revenue-sharing agreement, but the marketing carrier „leases“ the aircraft and its crew on behalf of the marketing carrier. There are also cases where it is simply a sales agreement with limited restrictions on the number of seats that the marketing carrier is allowed to sell on the operating flight. There is also a less common type of block space agreement, i.e.
a „soft“ layout of the block space. In this case, the marketing carrier may return unsold seats to the exporting institution. Parallel operation: A parallel code-sharing agreement is an operation between two airlines that use the same route. For example, if United Airlines and Delta Airlines fly from New York to Miami, a codeshare agreement between them can be characterized as a parallel operation. This is due to the fact that this code release is carried out in parallel with its own operations. Simply put in such a situation, the airlines will use the codes to each other as well as their own. There is a great deal of competition in the aviation sector over ticket sales strategies (also known as „seat reservation“) (revenue management, variable prices and geo-marketing). Consumer organizations and national trade ministries are critical of code sharing because it is supposed to cause confusion and transparency for passengers.  You can travel in the EU with your favourite airline (z.B in the US: Delta, AA, UA, US Airways). You book your ticket with this airline, but you must make sure it is a codeshare flight by one of the EU partners. In the event of a delay, you have the option of requesting a refund in accordance with EU Regulation 261/2004.