Universal Building Sets were released as early as 1966, but in 1973 the Basic LEGO sets became known as "Universal Building Sets". The sets were produced in two set number versions. One version was for produced for Europe, Britain, Australia and Canada (Canada started in 1974). The other version with the same box art but with different set numbers was for the USA. Most, but not all Universal Building sets between 1973 and 1981 were made for both geographic areas. Some of the sets were not sold in the USA. Universal Building Sets #2 thru #4 were first introduced in 1973 in continental Europe, Britain and Australia, followed by Canada in 1974. The USA versions under the numbers #105, #115 and #125 were also introduced in 1973.
Universal Building Sets sets were composed of an assortment of System bricks and building instructions that allowed to build various LEGO models related to a specific subject, in contrast to sets from other themes, such as LEGOLAND, which usually only contained pieces and instructions for one specific model. Other themes that were already present in that era were LEGOLAND and Trains.
The Universal Building Sets offered a greater range of a building possibilities and stirred the user's creativity to a larger extent than sets with just a single predefined model.