Wilhelm Karpenstein (born 24 May 1903 in Frankfurt am Main – died 2 May 1968 in Lauterbach, Hesse) was a German Nazi Party politician. He served as Gauleiter of Pomerania during the early days of the Third Reich.
Karpenstein was elected to the Reichstag in the 1930 election and served as a Nazi Party deputy until the end of the Second World War. He was appointed the party's Gauleiter in Pomerania in 1931.
Immediately after the Nazis came to power a significant amount of autonomy lay with the gauleiters and their radicalism threatened to disrupt the relationship between Adolf Hitler and the middle classes that had helped to ensure his election. Karpenstein was one of the few who did not offer this problem as he was conservative and pro-middle class. Nevertheless, he did not miss the opportunity to increase his personal power in the early days of Nazism and sought to make all of the churches, government officials and media outlets in Pomerania answerable to him directly.
Karpenstein however, despite not holding left-wing economic ideas, was too weak to control the dissident sentiments emerging from the Sturmabteilung in Pomerania, which was one of their power bases. As a result, Karpenstein was one of those to be purged during the Night of the Long Knives, although his lack of direct involvement with the SA meant that he was not killed but rather sacked in favour of Franz Schwede-Coburg. Ostensibly however Karpenstein was dismissed for his supposed links to Gregor Strasser and his failure to work with Hermann Göring.