Microarray gene expression analysis is high-throughput method in which many different sized DNA molecules are attached to solid surface in designated spots. These molecules are used for the discovery of specific RNA molecules isolated from various biological samples of interest. Core principle of this method is hybridization of complementary nucleotides (A-T and G-C), which leads to creation of double stranded nucleic acids. Gene expression differences in two groups of samples are discovered and quantificated by comparison of signal intensity values in microarray spots. Systemic analysis of data gathered in microarray gene expression measurement is performed by various bioinformatic methods such as group analysis, annotation analysis as well as network and pathway analysis. Expression comparison of all genes in different cells of the same individual or same cells of different individuals provides an insight into the mechanism responsible for development of a certain condition or disease.