Synthetic lethality occurs when the combination of two mutations leads to an inviable organism. Screens for synthetic lethal genetic interactions have been used extensively to identify genes whose products buffer one another or impinge on the same essential pathway. For the yeast Saccharomyces cerevisiae, we developed a method termed Synthetic Genetic Array (SGA) analysis, which offers an efficient approach for the systematic construction of double mutants and enables a global analysis of synthetic lethal genetic interactions. In a typical SGA screen, a query mutation is crossed to an ordered array of approx 5000 viable gene deletion mutants (representing approximately 80% of all yeast genes) such that meiotic progeny harboring both mutations can be scored for fitness defects. This array-based approach automates yeast genetic analysis in general and can be easily adapted for a number of different screens, including genetic suppression, plasmid shuffling, dosage lethality, or suppression.