Adapting tests across cultures is a common practice that has increased in all evaluation areas in recent years. We live in an increasingly multicultural and multilingual world in which the tests are used to support decision-making in the educational, clinical, organizational and other areas, so the adaptation of tests becomes a necessity. The main goal of this paper is to present the second edition of the guidelines of the International Test Commission (ITC) for adapting tests across cultures. A task force of six international experts reviewed the original guidelines proposed by the International Test Commission, taking into account the advances and developments of the field. As a result of the revision this new edition consists of twenty guidelines grouped into six sections: Precondition, test development, confirmation, administration, score scales and interpretation, and document. The different sections are reviewed, and the possible sources of error influencing the tests translation and adaptation analyzed. Twenty guidelines are proposed for translating and adapting tests across cultures. Finally we discuss the future perspectives of the guidelines in relation to the new developments in the field of psychological and educational assessment.