Flow cytometry is a sensitive and quantitative platform for the measurement of particle fluorescence. In flow cytometry, the particles in a sample flow in single file through a focused laser beam at rates of hundreds to thousands of particles per second. During the time each particle is in the laser beam, on the order of ten microseconds, one or more fluorescent dyes associated with that particle are excited. The fluorescence emitted from each particle is collected through a microscope objective, spectrally filtered, and detected with photomultiplier tubes. Flow cytometry is uniquely capable of the precise and quantitative molecular analysis of genomic sequence information, interactions between purified biomolecules and cellular function. Combined with automated sample handling for increased sample throughput, these features make flow cytometry a versatile platform with applications at many stages of drug discovery. Traditionally, the particles studied are cells, especially blood cells; flow cytometry is used extensively in immunology. This volume shows how flow cytometry is integrated into modern biotechnology, dealing with issues of throughput, content, sensitivity, and high throughput informatics with applications in genomics, proteomics and protein-protein interactions, drug discovery, vaccine development, plant and reproductive biology, pharmacology and toxicology, cell-cell interactions and protein engineering.