"Every piece of work in the shop moves; it may move on hooks, on overhead chains...it may travel on a moving platform, or it may go by gravity, but the point is that there is no lifting or trucking...No workman has anything to do with moving or lifting anything...Save ten steps a day for each of 12,000 employees, and you will have saved fifty miles of wasted motion and misspent energy." - Henry Ford
The idea for the assembly line came to Henry Ford when he visited a slaughter house.
"The assembly line was first used on a large scale by the meat-packing industries of Chicago and Cincinnati during the 1870s. These slaughterhouses used monorail trolleys to move suspended carcasses past a line of stationary workers, each of whom did one specific task. Contrary to most factories' lines in which products are gradually put together step-by-step, this first assembly line was in fact more of a "dis-assembly" line, since each worker butchered a piece of a diminishing animal. The apparent breakthroughs in efficiency and productivity that were achieved by these meat packers were not immediately realized by any other industry until the American industrialist Henry Ford (1863-1947) designed an assembly line in 1913 to manufacture his Model T automobiles." (http://science.jrank.org/pages/558/Assembly-Line-History.html)
The total time of assembly for a single car fell drastically:
"A stopwatch examination showed that it took 250 assemblers and 80 parts carriers working 9 hours a day for 26 days to complete 6,182 chassis and motors, an average of 12.5 man-hours for each chassis. The assembly line time fell to 93 minutes...Eventually the factory produced one car every 24 seconds." (Harold Evans, They Made America)
The assembly line revolutionized industry and paved the way for mass production in all manufacturing. Other businesses used the idea of the assembly line in their own factories, building appliances like stoves, refrigerators, radios, televisions, etc. The expansion in these industries created many jobs and helped build the American middle class.
"...by the end of World War I, the principle of continuous movement was sweeping mass-production industries of the world and was soon to become an integral part of modern industry." (http://science.jrank.org/pages/558/Assembly-Line-History.html)
The pictures in this slideshow below are of the Model T's assembly line (courtesy of thehenryford.org):