Stewart-MacDonald, commonly known as StewMac, is a supplier of tools, parts, and materials for building and repairing stringed instruments. Founded in 1968 by Kix Stewart and Bill MacDonald in Athens, Ohio, the company began by making banjos before shifting toward parts and kits. After acquiring the Waverly hardware line in the 1970s and hiring renowned guitar repairman Dan Erlewine in the mid-1980s, the company refocused on specialty tools for luthiers.

StewMac's catalog spans fret files, nut slotting saws, fretboard radius gauges, soldering stations, and other purpose-built repair tools, alongside tonewoods, pickups, pickguards, tuning machines, bridges, and complete guitar and bass kits under names like the Build Your Own line. The company also sells finishing supplies such as ColorTone lacquers and stains, and distributes educational video content through Dan Erlewine's long-running instructional series.

The company is widely recognized among amateur builders, professional repair techs, and guitar-building schools as a primary source for luthiery supplies in North America. Its website and YouTube channel host extensive free tutorials covering fretwork, setup, finishing, and electronics modification.

StewMac has 13 products cataloged on Equipboard, including Overdrive Effects Pedals, Fuzz Effects Pedals, and Tools. Their gear is featured by 4 artists, with the strongest followings in Rock, Folk, World, & Country, and Metal. Notable users include John Petrucci, Vince Gill, and Elizabeth Stokes.