A surgical instrument is a specially designed tool or device for performing specific actions of carrying out desired effects during a surgery or operation, such as modifying biological tissue , or to provide access for viewing it. Over time, many different kinds of surgical instruments and tools have been invented. Some surgical instruments are designed for general use in surgery, while others are designed for a specific procedure or surgery. Accordingly, the nomenclature of surgical instruments follows certain patterns, such as a description of the action it performs (for example, scalpel , hemostat ), the name of its inventor(s) (for example, the Kocher forceps),  or a compound scientific name related to the kind of surgery (for example, a tracheotome is a tool used to perform a tracheotomy ).
The expression surgical instrumentation is somewhat interchangeably used with surgical instruments, but its meaning in medical jargon is really the activity of providing assistance to a surgeon with the proper handling of surgical instruments during an operation, by a specialized professional, usually a surgical technologist or sometimes a nurse or radiographer .
There are several classes of surgical instruments:
- Graspers,  such as forcepts and sheet forts
- Clamps and occluders for blood vessels and other organs
- Retractors , used to spread open skin , ribs and other tissue
- Distractors, positioners and stereotactic devices
- Mechanical cutters ( scalpels , lancets , drill bits , rasps , trocars , Ligasure, Harmonic scalpel , surgical scissors , rongeurs etc.)
- Dilators and specula , for access to narrow passages or incisions
- Suction tips and tubes, for removal of bodily fluids
- Sealing devices, such as surgical staplers
- Irrigation and injection needles , tips and tubes, for introducing fluid
- Powered devices, such as drills , dermatomes
- Scopes and probes, including fiber optic endoscopes and tactile probes
- Carriers and appliers for optical , electronic and mechanical devices
- Ultrasound tissue disruptors , cryotomes and cutting laser guides
- Measurement devices, such as rulers and calipers
An important relative distinction, regarding surgical instruments, is the amount of bodily disruption or tissue trauma that their use might cause the patient. Terms relating to this issue are 'atraumatic' and minimally invasive . Minimally invasive systems are an important recent development in surgery.