Johann Voldemar Jannsen (16 May [O.S. 4 May] 1819 in Vändra, Kreis Pernau, Livonia, Russian Empire – 13 July [O.S. 1 July] 1890, in Tartu) was an Estonian journalist and poet active in Livonia.

He wrote the words of the patriotic song "Mu isamaa, mu õnn ja rõõm", which later became the national anthem of Estonia. He was the father of the poet Lydia Koidula. As the leader of the choral society which organised the first nationwide Song Festival in Tartu in 1869, Jannsen played a crucial role in the Estonian National Awakening.^[1]