Johann Jacob Roemer (8 January 1763, Zurich – 15 January 1819) was a physician and professor of botany in Zurich, Switzerland. He was also an entomologist.
With Austrian botanist Joseph August Schultes, he published the 16th edition of Carl Linnaeus' Systema Vegetabilium.
Roemer's Genera insectorum is a most attractive Swiss publication on entomology. The splendid hand-coloured plates were drawn and engraved by the Swiss artist J.R. Schellenberg, an entomologist himself and therefore familiar with structural details.
In 1793, he was elected a foreign member of the Royal Swedish Academy of Sciences. The botanical genus Roemeria from the family Papaveraceae is named after him.