The EF-Cambridge Open Language Database (EFCAMDAT) is a publicly available resource to facilitate second language research and teaching. It contains written samples from thousands of adult learners of English as a second language, world wide.

EFCAMDAT currently contains over 83 million words from 1 million assignments written by 174,000 learners, across a wide range of levels (CEFR stages A1-C2). This text corpus includes information on learner errors, part of speech, and grammatical relationships. Researchers can search for language patterns using a range of criteria, including learner nationality and level.

The resource is actively developed by the Department of Theoretical and Applied Linguistics at the University of Cambridge in partnership with Education First.