Quality assurance (QA) plays a critical role in high volume document digitization projects by making sure that the specified quality standard is reached under cost and time constraints. This paper takes a systematic view on this issue by summarizing and abstracting related existing work: quality bottlenecks and technical solutions throughout the whole processing pipeline, including cataloging, capture, image analysis and recognition, and error cascading; various strategies to conduct cost-effective QA, such as combination of auto-QA and manual QA, batch QA, special QA user interface, and open source QA. Notes: Published in and presented at the 2nd International Conference on Document Image Analysis for Libraries, 27-28 April 2006, Lyon, France 8 Pages