The main purpose of this research was to investigate whether or not customer relationship management had a significant influence on customer citizenship behaviors. This master thesis focuses on four different kinds of methods to invest in CRM. These are direct mailing, preferential treatment, interpersonal communication and offering tangible rewards. Of course, it is also important that the customers notice the efforts that a company is doing for them. This is called the perceived relationship investment. This is quite important because it influences the customer's perception of the relationship quality with the company. When a company has a positive perceived relationship investment, customers will be more likely to stay with the company. This can also be called customer retention. Another important aspect in this master thesis is the principle of Customer Citizenship Behavior (CCB) as a result of CRM. CCB is defined as 'the behavioral manifestations of customer engagement toward a firm after and beyond the purchase'. CCB can be measured through cooperation, compliance, feedback, customers helping other customers and through the spreading of word of mouth. Based on the results of this study it was clear that preferential treatment, interpersonal communication and tangible rewards had a statistically significant positive effect on the perceived relationship investment with the customers. Only the CRM technique of sending different kinds of direct mailings to the customers was considered not to be statistically significa