What are the wings and fuselage of an airliner made of?
Most modern planes are made mostly of aircraft aluminum. Or at least are skinned in aluminum. The spars and cross members may be made of other materials but I am under the impression they are mainly aluminum as well. Generally high stress areas like wing/fuselage joints may be made of more rigid materials like steel. Aircraft Spruce provides a nice break down of the various types of aluminum here. This answer to a similar question provides a nice break down.  

As the technology gets better and the facilities grow in both scale and ability, composites like carbon fiber have found their place in planes like the 787. Here is a break down for the 787 


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