How do they make those self-building cranes?

I can’t figure out how they make those internal building cranes, and how they get rid of them when they’re done. Many seem to be internal to the building. But most perplexing is how they seem to make them taller as the building grows. How do they build themselves up? I don’t even know how to search for such a thing on the net. any help here? xo C.

Tower Cranes from HowStuffWorks. Complete with nifty pictures of self-building cranes building themselves.

Clearly, at the SDMB, all of us are smarter than any of us. Thank you, Friedo. I guess I had figured it must be something like that, but didn’t have the term for it to look for it. Pretty cool. thanks. xo C.