Marine envenomation can result from discharging nematocysts (e.g. jellyfish, fire coral), puncturing spines (e.g. sea urchins, stingrays), or actual bites (e.g. blue octopus, sea snakes). This chapter addresses jellyfish envenomation. The emphasis is on pharmacotherapy. Antivenoms (or antivenins) may be an option for some species of sea snakes, jellyfish, stonefish, and antivenoms are known to have rapid and profound effects upon pain. For jellyfish stings worldwide, the most useful topical agent appears to be acetic acid topically applied in the 4-5% concentration found in vinegar. Acetic acid controls pain by deactivating nematocysts, thus limiting continued envenomation from attached stinging cells. The proteolytic enzyme papain has historically been reported to relieve jellyfish sting pain. Hot water immersion and opioids are also recommended for pedicellarial stings from sea urchins. There are no data on use of NSAIDs for marine envenomation.