Medical devices are often referred to as being invasive or non-invasive. Though invasiveness is relevant, and central, to how devices are understood and regarded in medicine and bioethics, a consensus concept or definition of invasiveness is lacking. To begin to address this problem, this essay explores four possible descriptive meanings of invasiveness: how devices are introduced to the body, where they are located in the body, whether they are foreign to the body, and how they change the body. An argument (...) is offered that invasiveness is not purely descriptive, but implicates normative concepts of danger, intrusion, and disruption. In light of this, a proposal is offered for how to understand use of the concept of invasiveness in discussions of medical devices. (shrink)