A surgical suture, also known as a stitch or stitches, is a medical device used to hold body tissues together and approximate wound edges after an injury or surgery. Application generally involves using a needle with an attached length of thread. There are numerous types of suture which differ by needle shape and size as well as thread material and characteristics. Selection of surgical suture should be determined by the characteristics and location of the wound or the specific body tissues being approximated.

In selecting the needle, thread, and suturing technique to use for a specific patient, a medical care provider must consider the tensile strength of the specific suture thread needed to efficiently hold the tissues together depending on the mechanical and shear forces acting on the wound as well as the thickness of the tissue being approximated. One must also consider the elasticity of the thread and ability to adapt to different tissues, as well as the memory of the thread material which lends to ease of use for the operator. Different suture characteristics lend way to differing degrees of tissue reaction and the operator must select a suture that minimizes the tissue reaction while still keeping with appropriate tensile strength.

Historically, surgeons used reusable needles with holes (called "eyes"), which must be threaded before use just as is done with a needle and thread prior to sewing fabric. The advantage of this is that any combination of thread and needle may be chosen to suit the job at hand. Swaged (or "atraumatic") needles with sutures consist of a pre-packed eyeless needle already attached (by swaging) to a specific length of suture thread. This saves time, and eliminates the most difficult threading of very fine needles and sutures.

Two additional benefits are reduced drag and less potential damage to friable tissue during suturing. In a swaged suture the thread is of narrower diameter than the needle, whereas it protrudes on both sides in an eyed needle. Being narrower, the thread in a swaged suture has less drag when passing through tissue than the needle, and, not protruding, is less likely to traumatize friable tissue, earning the combination the designation "atraumatic".^{[citation needed]}

There are several shapes of surgical needles. These include:^{[citation needed]}

The ski and canoe needle design allows curved needles to be straight enough to be used in laparoscopic surgery, where instruments are inserted into the abdominal cavity through narrow cannulas.

Needles may also be classified by their point geometry; examples include:

Finally, atraumatic needles may be permanently swaged to the suture or may be designed to come off the suture with a sharp straight tug. These "pop-offs" are commonly used for interrupted sutures, where each suture is only passed once and then tied.