The techniques by which the Egyptian pyramids were built is a matter of much speculation. Many theories have been developed and published, and new theories are still being created, but there is not yet any real consensus in the scientific world.
One factor that almost all agree on is that construction techniques developed over time; the earliest pyramids were built in different ways than the later ones.
Most construction theories are based on the idea that the pyramids were built by moving huge stones from a quarry and somehow dragging and lifting them into place. The disagreements center on the method by which the stones were conveyed and placed. There is, however, one other theory that is based on the "stones" being manufactured in-place from a kind of "limestone concrete".
In addition to the many theories as to the techniques involved, there are also disagreements as to the kind of workforce that was used. One theory, suggested by the Greeks, posits that slaves were forced to work until the pyramid was done. A more widely accepted theory in the modern era, however, suggests that the Great Pyramid of Egypt was built by hundreds of skilled workers who camped near the pyramids and worked for a salary or as a form of paying taxes until the construction was completed.