This Brief presents a new way of introducing relativity theory, in which
perplexing relativistic effects such as time dilation and Lorentz
contraction are explained prior to the discussion of
Lorentz-transformation. The notion of relativistic mass is shown to
contradict the spirit of relativity theory and the true significance of
the mass-energy relation is contrasted with the popular view of it. The
author discusses the twin paradox from the point of view of both
siblings. Last but not least, the fundamentals of general relativity are
described, including the recent Gravity Probe B experiment.