• Most airlines will only allow one carry-on bag in addition to one personal item. (1+1)
• Most bags within the 22 x 14 x 9 (45 linear inches) size restriction will be considered legal carry-on size with major domestic U.S. airlines
• Many airlines have sizing boxes at check-in desks within which your bag must fit.
• No knives or cutting instruments are allowed in carry-on baggage. 

Prohibited and permitted items.  (PDF file) from the Transportation Security Administration

NOTE: International travel may have different baggage allowances and restrictions depending on the destination.  Check with the specific airline

The fees for exceeding the restrictions on checked luggage can be quite expensive.  In recent months airlines have been more stringent in enforcing these policies

• Maximum Size is 62 linear inches (Length + Width + Height) 
• Many airlines have recently reduced the maximum weight of a checked piece from 70 lbs to 50 lbs.  Excess fees will apply if you exceed this weight restriction.
• Most airlines allow up to 2 checked bags for domestic US travel.
• Please note that the TSA now suggests that you do not lock your checked luggage.  If a screener has to open your bag then the locks may have to be broken.
• Most airlines will allow oversize, overweight, or additional baggage for an additional fee which varies depending on the situation. Please contact a particular airline for further info.
• Do not put film in checked baggage as the new screening machines may damage it.  Place it in your carry-on baggage.

NOTE: International travel may have different baggage allowances and restrictions depending on the destination.  Check with the specific airline