Abstract: Toy building blocks capable of assembly in any selected one of a variety of arrangements of contiguous blocks include a plurality of projections on one face of each block and a plurality of longitudinal and lateral channels on an opposite face of the block, the relative dimensions of the projections and the channels being such that the projections of one block are received in the channels of a contiguous block in the selected arrangement for sliding engagement in longitudinal and lateral directions while the projections are engaged with the channels for enabling alterations in the arrangement of contiguous blocks as the assembly is constructed. Preferably, the blocks are constructed of wood and the projections and channels are located in corresponding end-grain structures of the blocks.