Modular Functional Block System

The present disclosure is directed to the creation and/or manipulation of microfluidic systems and methods that can be formed in pre-existing modular blocks. Microfluidic paths can be formed in one or more blocks, and when multiple blocks are used, the blocks can be used together to form a path across the blocks. The paths can be sealed to prevent fluid leakage. The modular blocks can be readily available blocks which can then be individually customized to achieve various microfluidic design goals. The paths can be formed in outer surfaces of the blocks and/or disposed through a volume of the blocks. The modular blocks can have a uniform design across various block types, making it easy to reconfigure systems and/or remove and replace blocks and other components of the system. Methods for constructing such systems, and using such systems, are also provided.