The block is the main component for constructing models in the software. A variety of blocks are available inside of the block libraries. User-defined blocks can be written in C or OML. Blocks are defined as either reference or inline. A reference block refers to a block inside of a block library, while an inline block does not reference a library. A block can be categorized as a basic block, super block or programmable super block.

Graphically, a block occupies a rectangular region in a diagram even if the shape of the block is not rectangular. The rectangular boundaries of a block can be visible or not as defined in the block properties. Graphical elements within the boundaries can include an icon image, block name, and port names.