Johann Carl Friedrich Rellstab (27 February 1759 – 19 August 1813) was a German composer, writer, music publisher, and critic living in Berlin. Rellstab was a very influential figure in Berlin's musical life. In his youth he studied keyboard with Johann Friedrich Agricola and composition with Carl Friedrich Christian Fasch. He planned to continue his education with Carl Philipp Emanuel Bach in Hamburg, when in 1779 he had to take over the printing business of his father. Given his interest in music, Rellstab changed the focus of the business towards music and added a music lending library (in 1783) and a music publishing branch to the firm (ca. 1785). Later on, Rellstab also made instruments and sold other music supplies.
Rellstab's compositions include a Te Deum, a mass, numerous cantatas, lieder, and a singspiel,Die Apotheke, among other works.
His son Ludwig Rellstab (1799–1860) was also a music critic and a poet; some of whose verses were set by Franz Schubert in his Schwanengesang. Rellstab’s eldest daughter, Caroline Rellstab (1793–1813), was a singer noted for her extraordinary range extending to f‴. She sang at Breslau from 1811, and was particularly well known for her role as the Queen of the Night in Mozart’s Die Zauberflöte.