Corpora have had a significant impact on language assessment, contributing to the creation of valid instruments for evaluating second language (L2) proficiency. Different types of corpora provide empirical data that support language assessment theory and research as well as enhance the design, development, and validation of assessment instruments. Corpus linguistics facilitates the theoretical evolution of language proficiency constructs to encompass communicative competence and its components. It helps to identify key linguistic elements and skills necessary for effective language use across various domains, ensuring that assessment instruments align with authentic language practices. Furthermore, corpora prove invaluable resources in the development of test items and the refinement of scoring rubrics. They are also employed to validate existing tests against native speaker and L2 learner benchmarks. Finally, corpora and corpus analytical methods underpin the creation of automated scoring systems that enable valid, reliable and efficient assessment of test-takers’ written and spoken responses.