In almost all microarray technologies that are currently used, some type of surface chemistry serves as the interface between immobilized biomolecules and the solid support. Factors such as probe loading, spot morphology, and signal-to-noise ratio are all intimately linked to surface chemistry. Surface chemistry also significantly impacts important performance parameters such as three-dimensional structure of the immobilized biomolecules and nonspecific assay backgrounds. Here, an overview of the major types of surface chemistries currently used in printed microarrays is provided, with an emphasis on standard glass slide formats. The first part of this chapter focuses on DNA array surface chemistries, including both commercially fabricated and custom-made arrays. The second part of the chapter focuses on emerging protein, peptide, and carbohydrate array techniques. The intent is to provide the molecular biology researcher and bio-analytical or diagnostic specialist with a guide to the surface chemistry state-of-the-art for established and emerging array technologies.