Microarrays are considered as a technology in which 1000’s of nucleic acids are bound to the surface and are applied to measure the relative concentration of nucleic acid sequences in a mixture through hybridization and subsequent detection of hybridization events. This book is intended to present a critical overview of the current state of the art of the subject. This information can help researchers develop genetic testing to identify disease, and work on treatments to address specific genetic conditions. Gene libraries can also be stored for future reference and additional projects. It highlights on microarray gene expression analysis to evaluate cell type specific expression of targets relevant for immunotherapy of hematological malignancies. This book also proposes a new method for processing RNA-seq data that yields gene expression estimates that are much more similar to corresponding estimates from microarray data, hence greatly improving cross-platform comparability.