Underrepresentation in survey research is a common problem. People with a low economic status, people living in urbanized areas or lonely people are examples of groups hard to reach. Internet panel surveys are no exception and create even higher thresholds for participation. In the Netherlands an Internet panel of 5000 households was recruited based on recommendations from literature for optimal responses. This chapter discusses these recommendations and analyses why some groups are underrepresented in the panel. An in depth study will shine a light on how underrepresentation has been developed in the course of recruitment of the panel. Measures to reduce underrepresentation will be discussed and a thorough analysis will be conducted on the impact of results on a set of variables between the underrepresented groups and the panel.