The PLS-4 (Preschool Language Scale, 4th edition) is a psychometrically sound instrument constructed to assess language skills in children from birth to 6 years 11 months. It is a useful diagnostic and research tool that can be used to identify current comprehension and expressive language skills and can measure changes in language skills over time. The test is individually administered and includes tasks that assess skills in the areas of preverbal behaviors, as well as linguistic skills in the areas of semantics, morphology, syntax, integrative language skills, and preliteracy skills. Extensive reliability and validity evidence are presented. The test has been used extensively in research examining language development of young children from different home environments, children with identified medical conditions, and children participating in a variety of habilitation and intervention programs. Both the previous edition (PLS-3) and the new PLS-4 English and Spanish editions are used extensively in clinical, medical, and research settings to examine developmental language patterns of infants, toddlers, and preschoolers. (Contains 2 tables.)