This contract you received and which you may not have even known you entered, has many terms and conditions governing your flight that are often hidden in convoluted legal language. On the back of the typical ticket are fine-print paragraphs called "Conditions of Carriage". Included with these paragraphs is a statement that the airline has filed additional policies with the US Department of Transportation (DOT) about its liability limits and its promised services for passengers. Federal law mandates that any person who sells airline tickets – including airline employees at the airport or at an airline call center, as well as travel agents, travel websites and other retailers – must make a copy of the entire contract of carriage, including the aforementioned statements filed with the DOT, available to you upon request.
The contract of carriage is the basic document which governs the relationship between the airline and you, covering everything from boarding requirements and baggage limits to the compensation you are due if your flight is delayed. As mentioned before, the contract is usually written in very fine print and stilted toward the legally educated, but it is important. Read it. Each airline will have its own independent contract of carriage and while many use similar language, there will always be important differences also. You must always read the actual contract provided by the carrier before you file any complaints about your flight.
A piece of US legislature called the Federal Aviation Act protects your rights on domestic flights. This act gives the DOT authority to create and enforce regulations governing the responsibilities of airlines and the rights of passengers. While this act pre-empts most state laws that attempt to regulate airlines, some state statutes and common-law contract rules may still apply.
On international flights, your rights will largely fall under an international agreement called the Warsaw Convention. Almost all of the world nations that have functional airports now abide by the terms of this treaty. Like the Federal Aviation Act, it lists an airline's liability for any losses you may incur because your flight was delayed or your baggage was lost, delayed or damaged while you are engaged in international travel. If your ticket shows that you will be flying between countries that have adopted the Warsaw Convention or if, on the way to your final destination, you will stop over in a country that has adopted it, you meet this qualification.
An odd twist of the Warsaw Convention is that it applies, based on the way the ticket was issued, not on the actual flights. For example, if you booked a flight from Las Vegas to Tokyo and the flight crashes in California, you will be covered by the Warsaw Convention because it was your intent to fly internationally between the USA and Japan (both nations participate in this treaty). However, if your flight from New York to Oregon veers off course and crashes in Canada, the airline would not be bound by the Warsaw Convention.
Remember that the ticket you buy is in fact a legal contract and you are entering it willingly by purchasing it.