Phenotype MicroArray (PM) technology allows a biologist to test thousands of phenotypes of a cell line in a single experiment to gain a comprehensive overview of the metabolism, physiology, and pathway fluxes. It provides phenomic and metabolomic information that is complementary to genomic or proteomic analysis and often more easy to interpret and more useful. The PM technology platform is applicable to a wide range of cells including bacterial, fungal, or animal and enables metabolic analysis in the context of genotype-phenotype studies. For example, it can be used for (1) analyzing cells with mutations to determine the metabolic and physiologic effects of genetic differences, (2) studying and defining cell metabolism and metabolic regulation, (3) understanding the interplay of environment and hormonal signals on cell metabolism and physiology, (4) optimizing cell culture conditions in bioprocess development and optimization, and (5) examining and maintaining the stability of cell lines. Specific examples and discoveries will be presented to illustrate the many uses of this cell phenotyping technology.