What must organizations retain regarding handling complaints as per ISO 9001?

The requirement for organizations under ISO 9001 regarding handling complaints is to maintain records of complaints and their resolutions. This is crucial because these records provide essential evidence of the organization's commitment to quality management and continuous improvement. By documenting complaints and how they were resolved, organizations can identify trends, root causes of issues, and areas for improvement in their processes or products.

Such records support the organization's ability to demonstrate compliance with customer requirements and ISO standards, as they reflect how effectively the organization listens to and addresses customer concerns. Additionally, this documentation can serve as valuable input for internal audits, management reviews, and continuous improvement initiatives.

The other options do not fulfill the specific requirement for handling complaints in the context of ISO 9001. Complaints can come from various sources, including customers, stakeholders, or even internal feedback, so limiting records to only customer complaints would be incomplete. Suggestions for product improvement, while important, are not the same as complaints and do not require the same level of documentation. Annual summaries of quality performance do not focus on individual complaints and resolutions, making them less relevant to this specific requirement.