The first roller skis were originally manufactured in Sweden and then in Germany in the 1930's and were first used in Italy and Scandinavia.
Of course equipment evolved over time but the principle of using wheels to move forward and some sort of anti back-slipping system allowing to push off (in classic) has always been.
Skiroll.it website has a great photographic history of roller skiing with some incredible images of early equipment.
In the 1970s, something of a standard emerged and the first races took place. At this time all roller skis had one wheel in front and two wheels at the back. The metal frame was between 70 and 100 centimetres long.
The European Rollerski Federation was established around 1985, and the first European Championships were organized in the Netherlands in 1988.
Given the growth in roller skiing’s popularity, FIS recognized roller skiing as a distinct discipline in 1992 and the first roller skiing World Cup was held in 1993 and FIS World Championships in September 2000.
Nowadays, roller skiing is used as a primary mean of sport-specific training by skiers of all levels and regular races are held throughout summer and fall, in Europe in particular.