These guidelines describe considerations relevant to the assessment of test takers in or across countries or regions that are linguistically or culturally diverse. The guidelines were developed by a committee of experts to help inform test developers, psychometricians, test users, and test administrators about fairness issues in support of the fair and valid assessment of linguistically or culturally diverse populations. They are meant to apply to most, if not all, aspects of the development, administration, scoring, and use of assessments; and are intended to supplement other existing professional standards or guidelines for testing and assessment. That is, these guidelines focus on the types of adaptations and considerations to use when developing, reviewing, and interpreting items and test scores from tests administered to culturally and linguistically or culturally diverse populations. Other guidelines such as the "Standards for Educational and Psychological Testing" (AERA, APA, & NCME, 2014) or Guidelines for Best Practice in Cross-Cultural Surveys (Survey Research Center, 2016) may also be relevant to testing linguistically and culturally diverse populations. A glossary of terms and definitions is also provided.