SIGMA Brief 29 gives a short overview of the issue of common errors in public procurement. For the purposes of the Brief, errors are understood as infringements of public procurement rules and principles, regardless of the stage of the procedure. The Brief analyses the types of errors and their impact on the results of the public procurement procedure. It also gives a list and a short presentation (case studies) about the most common errors in public procurement. Finally, the Brief gives guidance on the potential means of mechanisms and procedures (review procedures, audits, checks) for detection and correction of errors.