A s a result of a rapidly increasing demand for accurate, cost-effective, and highly flexible multiplexed assay systems, the annual market for multiplex assays is currently billions of dollars and is expected to continue to grow exponentially. Presently, there exist two broad classes of surface-based multiplex platformsdthose using fixed planar surfaces (fixed arrays) and those that are particle-based (liquid arrays). We present here a description of an ''Arrayable Liquid Array'' platform, based on Encoded Sortable Particle (ESP) technology that combines many of the advantages of fixed and liquid arrays. ESPs have significant advantages in throughput, scalability, mixing efficiency, and flexibility over existing liquid array platforms while also incorporating the detection and manufacturing benefits of fixed arrays.