© 2018 Elsevier Inc. All rights reserved. The interpretation and application of clinical and laboratory data is an essential component of the job of a laboratory medicine practitioner or Transfusion Medicine director. Such data may be generated from assays within one's own laboratory or may arise in the form of published studies. Ultimately, such data will often be incorporated into routine practice and therefore, a clear understanding of data interpretation is critical. This chapter will provide a review of common scenarios faced by laboratorians and physicians where data interpretation is at the forefront of the clinical challenge.