A tricorder is a fictional handheld sensor that exists in the Star Trek universe. The tricorder is a multifunctional hand-held device that can perform environmental scans, data recording, and data analysis; hence the word "tricorder" to refer to the three functions of sensing, recording, and computing. In Star Trek stories the devices are issued by the fictional Starfleet organization.

The original physical prop for the tricorder was designed by Wah Chang and appeared in "The Man Trap" in 1966, the first Star Trek episode to air.

The tricorder of the 23rd century, as seen in Star Trek: The Original Series, is a black, rectangular device with a top-mounted rotating hood, two opening compartments, and a shoulder strap. The top pivots open, exposing a small screen and control buttons. When closed it resembles a portable tape recorder.

Three main variants appear in shows. The standard tricorder is a general-purpose device used primarily to scout unfamiliar areas, make detailed examination of living things, and record and review technical data. The medical tricorder is used by doctors to help diagnose diseases and collect bodily information about a patient; the key difference between this and a standard tricorder is a detachable hand-held high-resolution scanner stored in a compartment of the tricorder when not in use. The engineering tricorder is fine-tuned for starship engineering purposes. There are also many other lesser-used varieties of special-use tricorders.

The ship's medical variant employs a detachable "sensor probe" stored in the bottom compartment when not in use. The probe, although originally thought to have been fashioned from a spare salt shaker, was actually scratch-built for the show; the conical Danish salt shakers were set dressing, used as laser scalpels.

The 24th-century version of the tricorder introduced in Star Trek: The Next Generation is a small, gray, hand-held model with a flip-out panel to allow for a larger screen. This design was later refined with a slightly more angular appearance that was seen in most Next Generation–era movies as well as later seasons of Star Trek: Deep Space Nine and Voyager. In the post-Next Generation-era (Star Trek: Nemesis and Star Trek: Elite Force II), a newer tricorder was introduced. It is flatter, with a small flap that opens on top and a large touchscreen interface.

The tricorder prop for the original Star Trek series was designed and built by Wah Ming Chang, who created several futuristic props under contract. Some of his designs are considered to have been influential on later, real-world consumer electronics devices. For instance, his communicator inspired cell phone inventor Martin Cooper's desire to create his own form of mobile communication device. Many other companies followed this example and life-sized replicas remain popular collectibles today. The tricorder in The Next Generation was initially inspired by the HP-41C scientific calculator.

Software exists to make hand-held devices simulate a tricorder. Examples include Jeff Jetton's Tricorder for the PalmPilot; the Web application for the Pocket PC, iPhone, and iPod Touch; and an Android version.