  We review the origins of the Virtual Observatory (VO) concept, and the
current status of the efforts in this field. VO is the response of the
astronomical community to the challenges posed by the modern massive and
complex data sets. It is a framework in which information technology is
harnessed to organize, maintain, and explore the rich information content of
the exponentially growing data sets, and to enable a qualitatively new science
to be done with them. VO will become a complete, open, distributed, web-based
framework for astronomy of the early 21st century. A number of significant
efforts worldwide are now striving to convert this vision into reality. The
technological and methodological challenges posed by the information-rich
astronomy are also common to many other fields. We see a fundamental change in
the way all science is done, driven by the information technology revolution.
