This article is dedicated to the role of the Danish Language in the Kingdom of Denmark, the Faroe Islands and Greenland, in the light of the changes in Denmark’s ethnic composition throughout the past 200 years. Initially, this issue was raised in the 19th century, after Denmark suffered a number of tragic events: the defeat in the Napoleonic and the Second Schleswig Wars, and the dissolution of the Denmark–Norway Union. The loss of the territories led to the development of cultural, educational, and patriotic programmes in Denmark, in order to overcome the profound national crisis. The core question was: “Who can be considered a Dane?” Up to 1814, 25% of the population in the Denmark–Norway Union was German. After Norway separated, the percentage of Germans in Denmark rose to 40%. Then, Danish national self-identification was based on the formula: “Everyone who is not German is Danish,” and knowledge of the Danish language became the key factor. The Danish teacher and pastor N. F. S. Grundtvig developed the concept of Danish nationality – “Danishness” (Danskhed). According to this concept, national unity was built upon the native language, common national culture, and common national history. This concept is still widely acclaimed in modern Denmark. Various political parties constantly raise the question during fierce debates in parliament, in the media, and on social networks of “Who is a Dane in Denmark today?” The problem of knowledge of Danish language is the most important for Danish society, since the number of people who migrate to Denmark and bring with them their “alien” culture and values is constantly increasing. This article is based solely on Danish informational sources: official websites, encyclopaedias, media, discussion boards, and social networks.