National libraries throughout the world ensure that the nation’s published heritage is collected, catalogued, preserved, valorised and made accessible to present and future generations. In many countries a legal deposit system supports building the national collection. Although reaching a coverage of 100% remains an elusive dream, it is worth striving to achieve a comprehensive collection. This exploratory study first examines how to assess the completeness of the legal deposit collection in Belgium. Next, a chronological review of various methods and best practices applied in other countries leads to a number of insights and recommendations for a future assessment. Finally, a wide range of measures are presented to enhance compliance with legal deposit legislation and to innovate the monitoring process with the aim of improving the coverage of the Bibliography of Belgium.