From his seventh to his fourteenth year, Christian IV (1577-1648) wrote more than 800 Latin exercises to his preceptor, Hans Mikkelsen (1538-1601). They are formed as short essays or letters addressed to his teacher, fellow students and other associates, and give an interesting documentation of the didactic principles of Mikkelsen (based on those developed by the German reformator Johannes Sturm) and a vivid and charming picture of the life and thoughts of the royal child, striving to master the difficult conversational Latin he would need in his future rôle as King of Denmark and Norway &c. The article also discusses some editorial problems of a future edition of the Liber Compositionis Christiani Principis.