Tandem mass spectrometry has been the main driver behind a significant expansion in newborn screening programs. The ability to detect more than 40 conditions by a single test underscores the need to better understand the clinical and laboratory characteristics of the conditions being tested, and the complexity of pattern recognition and differential diagnoses of one or more elevated markers. The panel of conditions recommended by the American College of Medical Genetics, including 20 primary conditions and 22 secondary targets that are detectable by tandem mass spectrometry has been adopted as the standard of care in the vast majority of US states. The evolution of newborn screening is far from being idle as a large number of infectious, genetic, and metabolic conditions are currently under investigation at variable stages of test development and clinical validation. In the US, a formal process with oversight by the Advisory Committee on Heritable Disorders and Genetic Diseases in Newborns and Children has been established for nomination and evidence-based review of new candidate conditions. If approved, these conditions could be added to the uniform panel and consequently pave the way to large scale implementation.