Meta-evaluations can be conducted at many different times for different purposes: after an evaluation plan or design has been finalized, at periodic intervals during the evaluation to check progress and identify problems, and at the end of the evaluation to review findings and reports and to audit the evaluation procedures and conclusions. Having defined the purpose and the timing of the meta-evaluation, evaluators-or clients or sponsors if they have requested the meta-evaluation-can then determine whether to use internal and external reviewers.