A laser spark plug includes a laser light-producing device and a spark plug housing at the end of which facing the combustion chamber an injection lens for injecting laser light into the combustion chamber of an internal combustion engine is arranged. The spark plug housing includes a fastening zone for fastening the laser spark plug in a cylinder head of the internal combustion engine. A projection on the end of the spark plug housing facing the combustion chamber houses the injection lens. The outer diameter (D1) of the projection is smaller in the area of the injection lens than the outer diameter (D2) of the spark plug housing in the fastening zone.