WHO
  WHAT
  WHERE
  HOW
  WHY
  WHEN
  COST

Who?

You. Or at least people a lot like you. Space settlements will be a place for ordinary people.

Presently, with few exceptions, only highly trained and carefully selected astronauts go to space. Space settlement needs inexpensive, safe launch systems to deliver thousands, perhaps millions, of people into orbit. If this seems unrealistic, note that a hundred and fifty years ago no one had ever flown in an airplane, but today nearly 500 million people fly each year.

Some special groups might find space settlement particularly attractive: The handicapped could keep a settlement at zero-g to make wheelchairs and walkers unnecessary. Some religious groups might prefer to live away from "non-believers." Penal colonies might be created in orbit as they should be fairly escape proof. People who wish to experiment with very different social and political forms could get away from restrictive social norms.

Although some colonies may follow this model, it's reasonable to expect that the vast majority of space colonists will be ordinary people. Indeed, eventually most people in space settlements will be born there, and some day they may vastly exceed Earth's population. Based on the materials available, the human population in orbit could one day exceed ten trillion living in millions of space colonies with a combined living space hundreds of times the surface area of the Earth.