Johann Voldemar Jannsen (May 16, 1819 in Vändra, Livonia, Russian Empire – July 13, 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.