Travel agencies have been organized mostly since the start of commercial aviation although Thomas Cook was an early, pre-flight pioneer. Some travel agent companies operate with a chain of stores, such as Carlton Wagonlit; others are one store operations. Travel agencies do not sell airline tickets only; their services vary, and many of them sell more cruise ship packages than airline tickets. Most travel agencies also arrange car rental deals for their customers, and many concentrate on arranging charter or group trips to different destinations. For this, they deal with regular airlines, but many times, they also hire charter airlines. Many travel agencies work exclusively for a small group of airlines, cruise and car hire companies, and often, the logos of the companies they work with are displayed on the windows of the agency's office.

Travel agencies also deal with train and hotel companies. Generally, their goal is to try to fit an ideal schedule onto the requirements of each specific customer.

In the early era of model airplanes, airlines would have large plane models of their companies made and shipped to the travel agencies; these plane models are also available to the general public, but they are among the highest prized airline collectibles.

Many travel agencies feared their services would no longer be needed when many airlines and other travel companies began to sell directly to passengers over the Internet. They were afraid they would be victims of what management science experts call disintermediation.

Another worry was over the fact that airlines have been cutting back the commissions paid to travel agents on each tickets sold; the airlines feel that they are perfectly capable of dealing directly with their own passengers and do not need travel agents as much as in the past to fill seats.

Although many travel agents have since exited the industry, those who remain have managed to survive by promoting other travel products like cruise lines and train excursions, or by promoting their ability to aggressively research and assemble complex travel packages on a moment's notice (essentially acting as a very advanced concierge).

Airlines assign prices to their services in an attempt to maximize profitability. To do this well requires yield management technology and pricing flexibility.

They use differentiated pricing, a form of price discrimination, in order to sell air services at varying prices simultaneously to different segments. Factors influencing the price include the days remaining until departure, the current booked load factor, the forecast of total demand by price point, competitive pricing in force, and variations by day of week of departure and by time of day.

A complicating factor is that of origin-destination control ("O&D control"). Someone purchasing a ticket from say, Melbourne to Sydney for $A200 is competing with someone else who wants to fly Melbourne to Los Angeles through Sydney on the same airplane, and who is willing to pay $A1400. Should the airline prefer the $A1400 passenger, or the $A200 passenger + a possible Sydney-Los Angeles passenger willing to pay $A1300? Airlines have to make hundreds of thousands of similar pricing decisions daily in their markets.

In contrast, low fare carriers usually offer straightforward, preannounced, simple prices. They can do this by quoting prices for each leg of a trip; passengers simply add them together to construct a full journey.

The advent of advanced computerized reservations systems in the late 1970s, most notably Sabre, allowed airlines to easily perform cost-benefit analyses on different pricing structures, leading to almost perfect price discrimination in some cases (that is, filling each seat on an aircraft at the highest price that can be charged without driving the consumer elsewhere). The intense nature of airfare pricing has led to the term "fare war" to describe efforts by airlines to undercut other airlines on competitive routes.

Computers also allow airlines to predict, with some accuracy, how many passengers will actually fly after making a reservation to fly. This allows airlines to overbook their flights enough to fill the aircraft while accounting for "no-shows," but not enough (in most cases) to force paying passengers off the aircraft for lack of seats. Since an average of 1/3 of all seats are flown empty, stimulative pricing for low demand flights coupled with overbooking on high demand flights can help reduce this figure.- from Wikipedia.org