The remora (/ˈrɛmərə/), sometimes called suckerfish or sharksucker, is any of a family (Echeneidae) of ray-finned fish in the order Carangiformes. Depending on species, they grow to 30–110 cm (12–43 in) long. Their distinctive first dorsal fins take the form of a modified oval, sucker-like organ with slat-like structures that open and close to create suction and take a firm hold against the skin of larger marine animals. The disk is made up of stout, flexible membranes that can be raised and lowered to generate suction. By sliding backward, the remora can increase the suction, or it can release itself by swimming forward. Remoras sometimes attach to small boats, and have been observed attaching to divers as well. They swim well on their own, with a sinuous, or curved, motion.

Remoras are thought to be most closely related to the cobia and the dolphinfish, two other elongate members of the suborder Carangoidei. Together, they are thought to comprise the superfamily Echeneoidea. In some treatments, the Echeneoidea is instead restricted to just the remoras and Opisthomyzon.

The earliest remora-like fish in the fossil record is Opisthomyzon from the Early Oligocene of Switzerland. This taxon appears to be closely related to modern remoras and shares several of the iconic traits present in modern remoras, including an adhesive disk (although located posterior to the head rather than directly on it). However, due to its distinctive morphological features from modern remoras, it is placed in its own family, Opisthomyzonidae.

Also known from the Early Oligocene is the earliest true remora in the fossil record, Echeneis carpathica from Poland. From later in the Oligocene, the extinct genus Oligoremora is known from the Chattian of Germany.

Remora front dorsal fins have evolved to enable them to adhere by suction to smooth surfaces, and they spend most of their lives clinging to a host animal such as a whale, turtle, shark or ray. It is probably a mutualistic arrangement as the remora can move around on the host, removing ectoparasites and loose flakes of skin, while benefiting from the protection provided by the host and the constant flow of water across its gills. Although many believe that remoras feed on particulate matter from the host's meals, some posit alternative theories; they claim their diets to be composed primarily of host feces. Further research is needed to validate the extent of this alternative feeding mechanism.

Remoras are tropical open-ocean dwellers, but are occasionally found in temperate or coastal waters if they have attached to large fish that have wandered into these areas. In the mid-Atlantic Ocean, spawning usually takes place in June and July; in the Mediterranean Sea, it occurs in August and September. The sucking disc begins to show when the young fish are about 1 cm (0.4 in) long. When the remora reaches about 3 cm (1.2 in), the disc is fully formed and the remora can then attach to other animals. The remora's lower jaw projects beyond the upper, and the animal lacks a swim bladder.

Some remoras associate with specific host species. They are commonly found attached to sharks, manta rays, whales, turtles, and dugongs, hence the common names "sharksucker" and "whalesucker". Smaller remoras also fasten onto fish such as tuna and swordfish, and some of the smallest remoras travel in the mouths or gills of large manta rays, ocean sunfish, swordfish and sailfish.

The relationship between a remora and its host is most often taken to be one of commensalism, specifically phoresy.