LEGO System i Leg Sets

System i Leg, which translates to System of Play, was the natural progress of LEGO Mursten and is the foundation of L:EGO sets today. Designed by Godtfred Kirk Christiansen who organized the existing LEGO Mursten sets and modeled new designs around a single, common theme - a townscape or street scene. After nearly a year of development the result was the LEGO Mursten System i Leg (System of Play). The System i Leg was unveiled at the Nürnburg Toy Fair in February 1955. The original Automatic Binding Bricks sets and then LEGO Mursten sets were continued to be manufactured under the System i Leg theme.

The theme originally consisted of the existing 700 series LEGO Mursten sets and several new HO scale accessories but over the next several years the system was greatly expanded with both new building sets and many HO scale accessory sets. The system allowed children to not only to build architectural models, which had always been featured in LEGO catalogs, but added play value with a completely new series of cars, trucks, and street signs.