Heinrich Friedrich Ludwig Rellstab (April 13, 1799–November 27, 1860) was a German poet and music critic. He was born and died in Berlin. He was the son of the music publisher and composer Johann Carl Friedrich Rellstab.

The first seven songs of Franz Schubert's Schwanengesang have words by Rellstab. His work was also set to music by Franz Liszt. He is also known to have given Ludwig van Beethoven's opus 27 no. 2 sonata its famous but inaccurate nickname, Moonlight Sonata. It is actually music of funereal lamentation, set deliberately by Beethoven in the lamenting key of C-sharp minor.