The Danish ethnic minority in Southern Schleswig, Germany, has existed by this name since 1920, when the Schleswig Plebiscite split German-ruled Schleswig into two parts: Northern Schleswig, with a Danish majority and a German minority was united with Denmark, while Southern Schleswig remained a part of Germany and had a German majority and Danish and Frisian minority populations. Their historic roots go back to the beginning of Danish settlement after the emigration of the Angles. One of the most common names they use to describe themselves is danske sydslesvigere (Danish South Schleswigians).
Denmark has continued to support the minority financially. Danish schools and organizations have been run in Flensburg since 1920, and since 1926 throughout the greater region. Before the adoption of the democratic Weimar Constitution it was not allowed to teach in another language than German in school (apart from religious education lessons).
Membership in Danish or German ethnicity has been fluid since the first national conflicts in the region about 1848, as objective criteria such as language to distinguish a German Schleswigian from a Danish are not taken into account. German law prohibits government registration of persons due to their ethnic origins; besides, membership in Germany's ethnic minorities is based on self-identification as is generally the universal case with ethnicity. The first ethnic Danes settled in Southern Schleswig in the 7th century. One of the first Danish cities, Hedeby, were founded in about 800. The Danevirke between Hollingstedt and the Eckernförde bay was a Danish border wall towards Germany. Schleswig (Southern Jutland) was in the Viking Age still a direct part of the Kingdom of Denmark. First in the 13th century it became a fiefdom of Denmark. Old Danish were spoken north of a line between the Eider, Treene and Eckernförde Bay. But in the 17th, 18th and up to the 19th centuries there was a language shift from Danish and North Frisian dialects to Low German and later to High German as common speech in Southern Schleswig. Many German-minded Schleswigians have therefore ethnic Danish roots. At the same time there grew a conflict between German and Danish National Liberals, that culminated in two German-Danish wars in the 19th century. After the Second Schleswig War Schleswig became for the first time part of a German state. After a plebiscite in 1920 Northern Schleswig was officially reunited with Denmark, while Southern Schleswig remained a part of Germany.
Also, the 1955 Copenhagen-Bonn Declarations explicitly state that an individual's membership of the German minority in Denmark or the Danish minority in Germany may not be a matter of scrutiny from the respective governments. Also many Schleswigians on both sides of the border are of mixed extraction. While after the 1920-plebiscite between 6,000 and 20,000 Danes found themselves in Southern Schleswig  and even more than 3,000 out of 20,000 people had voted for Denmark in 1920, about 3 000 were organised in the association (Slesvigsk Forening), but this number declined to only about the same 3,000 under National Socialism by the end of the World War II.
After World War II, many Germans and German-speaking people of various backgrounds chose to join the Danish minority for purely opportunistic reasons (i.e. regardless of their actual ethnic origin). They were hoping to join the more prosperous Denmark, partly caused by a wish to live in a free and democratic country, partly motivated by social hardships in the aftermath of World War II, particularly with the influx of more than one million German refugees into Schleswig-Holstein. A high proportion of the 'new Danes' had a lower-class background, while only very few of the old elite changed their self-professed ethnic identity. As the Danish government provided food aid to the minority during 1945–49, this contingent became derogatorily known as "Speckdänen (de)", ("bacon Danes"). At the end of 1946 the minority had thus reached a membership of 62,000 and in 1948 78,000, many of whom were monolingual German-speakers with typical German names. On the other hand, many German-minded inhabitants had and have ethnic Danish ancestors and typical Nordic surnames. The Danish political party got almost 99,500 votes in 1947.
However, the Danish government and the British Occupation Zone governors both opposed Southern Schleswig rejoining the Kingdom, and a referendum was never held in Southern Schleswig. Controversy over the issue divided two of the main Danish parties, and both Venstre leader and Prime Minister Knud Kristensen and Conservative leader John Christmas Møller ultimately broke with their respective parties over the issue. In 1953 the so-called Programm Nord (Northern Programme) was set up by the Schleswig-Holstein state government to help the area economically. This caused the Danish minority to decline until the 1970s. Since then, the minority has slowly been gaining size. Today it numbers around 50,000, although only a number of between 8,000 and 10,000 are assumed to speak Danish in everyday life. Between 10,000 and 20,000 of them have Danish as their mother tongue.
The fluctuation of the Danish minority is reflected also in the respective literature that describes the local phenomenon of changing national self-identification with the term "New Danes". The number of Danes vary e.g. in "Fischers Weltalmanach" (Fischer's World Almanac), having been specified with 30,000 until 1994, then having risen up to 60,000 in 1995 and finally having been reduced to 50,000 since the year 2001. The source for the number of Danes in the minority is the ,,Beratender Ausschuß für Fragen der dänischen Minderheit beim Bundesminister des Innern", a consulting commission in the Ministry of the Interior, composed of representatives of the ministry itself, two members of each party in the German parliament, the Commissary for Minorities of Schleswig-Holstein and three members of Danish party (2) and association (1). The numbers of members and also of users of the minority's organisations (sport clubs, culture associations, playschools, schools, libraries, etc.) and likewise the number of electors of the Danish party are considered to indicate people being Danish, although it has to be mentioned that the data records of the organisations are not linked among themselves and – what is more – the majority of users and members do not have Danish as their mother tongue.
The Danish minority is represented by the South Schleswig Voter Federation (SSW) in the Diet (Landtag) of Schleswig-Holstein. The SSW is not subject to the general requirement of passing a 5% vote threshold in order to receive proportional seats in the state parliament. In the most recent 2012 election, the SSW received 4.6% of the vote and three seats. The SSW is also represented in several municipal councils.