Despite new developments in molecular techniques and better knowledge on lung cancer tumor biology, many genetic alterations associated with the development and progression of lung carcinogenesis still remain unclear. Although the development of targeted agents has improved response rates and survival, lung cancer has a very high mortality rate, even for early stages. Thus, there is a greater need for other mechanisms or technologies that may help us diagnose, predict, and treat patients with lung cancer in a more effective way. One of these technologies has been the use of genomics. Some of the available genomic technologies include single-nucleotide polymorphism analysis, high-throughput capillary sequencing, serial analysis of gene expression, and gene expression arrays. DNA microarray analysis is capable of discovering changes in DNA expression within the neoplastic tumor. Thus, gene expression array could help us to decipher the complexity and interaction of different oncogenic pathways and, hence, could contribute to the selection of better targeted agents on an individual basis rather than a general and nonspecific approach as it has been done for many decades. Several studies initiated a few years ago have started to produce fruitful results. Herein, we review the role of gene expression profiling in lung cancer as a diagnostic tool, predictive and prognostic biomarker, and its potential use for a "personalized" medicine in the years to come.