Abstract: A toy building block base comprises a flexible elongate body strip having a first major surface along a length of the strip that includes either an array of projections extending from the first major surface or an array of recesses set into the first major surface. The projections or recesses form a mating arrangement for co-operant toy building blocks. An opposite, second major surface has a shallow flat-bottomed longitudinal recess with a longitudinal adhesive layer by which the body strip can be attached to a support surface. The body strip includes no more than four projections or recesses across its width and has a length of at least 200 mm. The entire body strip is made from a homogenous flexible plastics material with a durometer value of between 35 and 80 according to the ASTM D2240 standard's type A durometer scale.