Microarrays have become an extremely important research tool for life science researchers and are also beginning to be used in diagnostic, treatment and monitoring applications. This article provides a detailed description of microarrays prepared by in situ synthesis, deposition using microspotting methods, nonplanar bead arrays, flow-through microarrays, optical fiber bundle arrays and nanobarcodes. The problems and challenges in the development of microarrays, development of standards and diagnostic microarrays are described. Tables summarizing the vendor list of various derivatized microarray surfaces, commercially sold premade microarrays, bead arrays and unique microarray products in development are also included.