The standard relativistic theory of accelerated reference frames in Minkowski
spacetime is described. The measurements of accelerated observers are
considered and the limitations of the standard theory, based on the hypothesis
of locality, are pointed out. The physical principles of the nonlocal theory of
accelerated observers are presented. The implications of the nonlocal theory
are briefly discussed.Comment: LaTeX file, no figures, 9 pages, to appear in: "Advances in General
Relativity and Cosmology", edited by G. Ferrarese, Pitagora (Bologna), 200
