Microfluidics is the minitiarization of fluid-based biochemistry to very small volumes such that a large series of chemical reactions can be performed in parallel in a microarray format (see Microarray). The essential issue with developing microfluidics-based devices is the ability to maintain adequate access to the solutions needed in each element of the array, delivered both spatially (to each addressable location in the array) and temporally (at the appropriate time in the reaction). Other issues include scaling-down problems that occur with biochemical reactions, such as diffusion rates and heating. Several companies have now manufactured microfluidics devices (“labs-on-a-chip”) that allow the high-throughput chemistries needed in screening, synthesis and probing of biological molecules. Because a large number of chemistries are supported, the arrays are customizable (“programmable”) to perform a variety of functions. Examples of microfluidics-based applications include screening of biological targets, synthesis of combinatorial libraries, synthesis of DNA oligomers, and analysis of polymorphic proteins, all of which can be performed in large high-throughput parallel arrays because of microfluidics.