Customers are vital to any organization and system, and must therefore be considered when seeking to improve. However, how to improve with regard to the customer, is not clear, and the knowledge is spread over several research fields, making it difficult for researchers and practitioners to comprehend. The purpose of this literature review is to show how customer-related improvements are described in the literature and how the research is performed. 666 articles were screened, resulting in 99 coded and analysed articles. The study concludes that there is a lack of understanding when it comes to the process of how to improve and that both practitioners and academics should focus more on the system level. It is also seen that by involving the customer in the improvement process, the improvement is more likely to succeed. The article concludes that there is a need for future research which are conceptual, longitudinal, and are addressing actual improvements, not just potential. From the practitioners’ point of view, the article is proposing an increased focus on customer-related improvements which address aspects concerning people, such as employee competence and work environment, and reward systems, rather than strategy and processes to improve the potential benefits.