CELTA is an initial teacher training qualification for teaching English as a second or foreign language (ESL and EFL). It is provided by Cambridge Assessment English through authorised Cambridge English Teaching Qualification centres and can be taken either full-time or part-time. CELTA was developed to be suitable both for those interested in Teaching English as a Foreign Language (TEFL) and for Teaching English to the Speakers of Other Languages (TESOL). The full name of the course was originally the Certificate in English Language Teaching to Adults and is still referred to in this way by some course providers. However, in 2011 the qualification title was amended on the Ofqual register to the Cambridge English Level 5 Certificate In Teaching English to Speakers of Other Languages (CELTA) in order to reflect that the wider range of students that teachers might have, including younger learners.

CELTA is designed for candidates with little or no previous English language teaching (ELT) experience. It is also taken by candidates with some teaching experience who have received little practical teacher training or who wish to gain internationally recognised qualification. Candidates should have English language skills equivalent to at least C1 of the Common European Framework of Reference for Languages (CEFR) or an IELTS score of 7.

CELTA gives equal emphasis to theory and practice. The strong practical element demonstrates to employers that successful candidates have the skills to succeed in the classroom. Courses can be taken full-time or part-time through one of three modes of delivery: fully face-to-face, in a blended format that combines on-line self-study with practical teaching experience, or fully online, with teaching practice and input all being delivered online through a video conferencing platform such as Zoom. A full-time, face-to-face course typically lasts between four and five weeks. CELTA is a continuous assessment course (i.e. participants are assessed throughout the course) leading to a certificate qualification.

Candidates who successfully complete the course can start working in a variety of English language teaching contexts around the world. CELTA is regulated at Level 5 of the Qualifications and Credit Framework for England, Wales and N. Ireland and is suitable for teachers at Foundation and Developing level on the Cambridge English Teaching Framework.