Language testing has been defined as one of the core areas of applied linguistics because it tackles two of its fundamental issues: the need to define and reflect on the appropriateness of Second Language Acquisition models and constructs by data analysis from language tests and the importance of facing the ethical challenge deriving from the social and political role language tests play nowadays. Language testing has thus a twofold impact in a variety of contexts. In the first instance, it constitutes a scientific impulse for which research is needed to develop and implement the technical design of tests. Secondly, language testing has also become subject of debating because the use and interpretation of test results introduce ethical issues concerning the concept of ‘fairness’ in the construction, administration, evaluation and interpretation of language tests. In fact, language tests are always designed and used to make decisions on the basis of a process in which information about test takers is gathered from an observed performance under test conditions. This inevitably leads to the development of codes of ethics in educational testing environments and to the elaboration of theories of validity and validation.