The Internet, a network of computers covering the entire planet, allows people to access almost any information located anywhere in the world at any time. Its effects on business, communication, economy, entertainment and even politics are profound. The Internet may not have changed the world as much as the plow, but it's probably on par with the steam engine or automobile.
DARPA (Defense Advanced Research Projects Agency), the research and development arm of the U.S. military, created ARPANET in the late 1960s. This network of computer-to-computer connections was intended for military and academic research. Other computer networks began to cross the globe in the next few years, and by the late 1970s computer scientists had created a single protocol, TCP/IP, that would allow computers on any network to communicate with computers on other networks. This was, essentially, the birth of the Internet, but it took 10 or so years for various other networks in the world to adopt the new protocol, making the Internet truly global.
The Internet is such a powerful invention that we've probably only begun to see the effects it will have on the world. The ability to diffuse and recombine information with such efficiency could accelerate the rate at which further world-changing inventions are created. At the same time, some fear that our ability to communicate, work, play and do business via the Internet breaks down our ties to local communities and causes us to become socially isolated. Like any invention, the good or ill it accomplishes will come from how we choose to use it.