A Product Backlog is an ever-evolving list of product requirements that bring value to the product by meeting customer needs. It should be the single source of requirements for any changes to be made to the product. The Product Owner is typically in charge of building, ordering and maintaining the Product Backlog. As the product evolves, the Product Backlog gets more complex. The Product Backlog refinement consists in adding details, time estimates and prioritization order of the different items. All items are reviewed and revised. Prioritization is often done with the customer to order items by business value. Agile team typically create a sub-backlog containing the top entries for each development iteration known as an iteration backlog or sprint backlog.