This chapter is based on our more than 30 years of experience empowering businesses everywhere to compete and thrive in the modern data-driven economy. We at dunnhumby have enabled retailers all around the world to grow and reimagine themselves by understanding their customers and becoming advocates and champions for them. Using customer insight in retail is all about decomposing the sales line to uncover opportunities for growth and identify weaknesses that cause performance drag. Traditional analytics focuses on unprofitable stores, category performance and regional differences. Customer insight transforms this approach, first by enhancing and deepening the level of understanding possible and then by bringing the power of machine learning to model the future evolution of behaviours and sales.