Brüel & Kjær is a Danish engineering company founded in 1942 by Per Vilhelm Brüel and Viggo Kjær, and headquartered in Nærum, near Copenhagen. The company specializes in sound and vibration measurement instrumentation, including precision measurement microphones, sound level meters, frequency analyzers, calibrators, and acoustic test systems. Its measurement microphones — which the company began manufacturing in 1945, with its 1/2-inch condenser capsules becoming an industry reference by the 1970s — are widely used as calibration standards in acoustic research, product development, automotive NVH testing, and environmental noise assessment.

While Brüel & Kjær's core business is scientific measurement rather than music production, its hardware has long intersected with pro audio work involving room tuning, loudspeaker design, and acoustic analysis. The company's pro audio division was spun off in 1992 to form DPA Microphones, but the B&K name itself remains associated with high-precision reference capsules and test gear used in studio design, mastering rooms, and research-grade recording applications.

Brüel & Kjær has 3 products cataloged on Equipboard, including Condenser Microphones and Effects Processors. Their gear is featured by 6 artists, with the strongest followings in Rock, Pop, and Electronic. Notable users include Bob Dylan, Sara Bareilles, and Suzanne Ciani.