The musical instruments of the 21st century and those of earlier times differ in many respects, be it their appearance, their technical functionality, their playing technique, or their sounds. And as they have changed, so too have our understandings of what a musical instrument is. The lacking precision of the current notion of the instrument and its incompatibility with contemporary instrumental forms are consequences of a technocultural process that raises fundamental questions about the identity of the musical instrument: When (and why) is something a musical instrument—and when (and why) is it not? In order to grasp the slight differences between the yet-to-be-defined instrumental and the assumed other, it seems reasonable to speak of instrumentality when denoting this particular specificity that instruments are supposed to feature. The present contribution seeks to prepare the ground for a reflective discussion on the concept of instrumentality and the underlying theoretical problem by considering not only the differences, but also the similarities between traditional and electronic musical instruments. Using a couple of different approaches to and views on the concept and defining a number of criteria of instrumentality, it eventually yields a picture of musical instruments that connects the contemporary ones with those known for centuries.