In the last two decades, many organizations have been using Lean Manufacturing to be competitive in the global market. Lean emerged as the western version of the Toyota Production System. TPS is a production management system focused on the flow of the product through the whole manufacturing process. The goal is to eliminate as many activities as possible that do not add value to the final product. Due to the soft effects of Lean improvements, one current issue is evaluating the economic benefit of these improvements. Literature about the financial impact of implementing Lean and the cost associated to this implementation are very scarce. One of the more critical solutions to measure efforts and resources related to a quality improvement has been Cost of Quality. Since COQ is an important measure from the management standpoint, this paper develops a literature review and a conceptual framework of Lean Process Improvement and the cost in quality. Copyright, American Society for Engineering Management, 2011.