Flow cytometers are instruments that can determine multiparameter data simultaneously and have a great potential in providing unique information about cells. To transfer this potential to the clinical laboratory, the development and the proper use of standards and calibrators are required to ensure comparability and reproducibility of data from different flow cytometers. Although there are a number of types of standards for flow cytometry, each has its specifically designed purpose to ensure that data from this complex instrument are accurate, precise, and reproducible among instruments over time.