The concept of customer data in marketing encompasses all customer information that a company can collect and use. Previously, this data was primarily limited to information gathered during purchases, loyalty program data, and sometimes consumption data (energy, telephone, etc.). However, with the proliferation and digitization of communication channels, the quantity and variety of data available for each customer have exploded. Analyzing this customer data allows for a better understanding of customers and the personalization of interactions across various marketing and advertising channels. By avoiding generalizations, data collection and analysis ideally aim to achieve in-depth customer knowledge, thus fostering an optimal user experience. The methods for collecting, storing, and activating customer data have evolved significantly, moving from simple customer files to sophisticated tools such as CRMs or other dedicated platforms. It is imperative that the collection and use of customer data comply with the recommendations of the CNIL (French Data Protection Authority) and all applicable regulations. A clear explanation of the process for collecting and using customer data is essential to ensure transparency and compliance.