A gunsmith is a person who repairs, modifies, designs, or builds guns. The occupation differs from an armorer, who usually replaces only worn parts in standard firearms. Gunsmiths do modifications and changes to a firearm that may require a very high level of craftsmanship, requiring the skills of a top-level machinist, a very skilled woodworker, and even an engineer. Gunsmiths perform factory-level repairs and renovations to restore well-used or deteriorated firearms to new condition. They may make alterations to adapt sporting guns to better fit the individual shooter that may require extensive modifications to the firearm's stocks and metal parts. Repairs and redesigns may require fabrication and fitting of unavailable parts and assemblies constructed by smiths themselves. Gunsmiths may also renew metal finishes or apply decorative carvings or engravings to guns. Many gun shops offer gunsmithing services on the premises.

Gunsmiths may be employed in:

To pursue the entirety of this trade, a gunsmith must possess skills as a parts fabricator, a metalworker or blacksmith, a woodworker and an artisan; be knowledgeable in shop mathematics, ballistics, chemistry, and materials engineering; be knowledgeable in the use and application of a variety of hand, power, and machinists tools and measuring devices. Those who are (self-) employed in small gunsmith shops must also possess skills as small business operators; work effectively with a wide variety of customers; and remain abreast of, and comply with federal, state, and local laws, ordinances, and requirements.^{[citation needed]}

Due to the great breadth of subject matter to be mastered, many gunsmiths specialize in only a few of the skills required of the general gunsmith. Alternatively, some gunsmiths learn many of the skills of the trade but only apply them to a few weapon types (e.g., only pistols, only shotguns, only specific brands or models).

The primary responsibility of a gunsmith is to ensure that guns work and function safely. Gunsmiths accomplish this by always properly observing and demonstrating gun safety in their handling procedures, both in their own actions and the actions of their customers and the people around them.

They accomplish that task secondly by inspecting guns to ensure safe mechanical operation. Gunsmiths use their in-depth knowledge of firearms and manufacturer's gun schematics to guide inspections: repairing deficiencies, notifying customers of unsafe conditions, or preventing catastrophic failures.

Some of the conditions a gunsmith looks for when inspecting a firearm brought to them for repairs are improper assembly, missing parts, cracks, bore obstruction, improper headspace, improper timing, safety malfunctions, worn sear edges, and deformed firing pin tips, among other problems.

*Gun schematics, also referred to as firearm schematics, are technical diagrams that display a firearm's internal workings and parts. These schematics usually feature detailed illustrations of significant components like the barrel, receiver, trigger assembly, and magazine. They are often used by gun enthusiasts, manufacturers, and gunsmiths to diagnose and fix problems that may arise with the firearm.