Increasingly, global society is focused on the harm caused by material accessed on the internet. Individuals of all ages and backgrounds–policy makers, academics, politicians, mental health professionals, medical professionals and the general public–are seeking to understand the processes that govern the relationship between exposure to harmful content online and later harmful cognitions and behaviors. Several commentators have placed into stark focus several questions surrounding the use (and misuse) of the internet, and prevention of harm from it. Three issues come immediately to mind: First, what can be done to prevent the manifestation of harmful activities stemming from being online? Second, what is the underlying relationship between harmful material accessed online, and harmful behavioral outcomes? And third, what is the best approach (and how to we know what the “best” is) to prevent the manifestation of harmful behavior stemming from harmful content online? Rather than looking at each of these issues as a stovepipe, and seeking to answer each in isolation, in this chapter we adopt an integrationist perspective on the issue of preventing online harm online. Specifically, we will look at the theories of how and why exposure to extreme and harmful material online can cause negative real-world outcomes. We focus on the innovative Google-led program Jigsaw, 1 to explore the many and varied approaches that can be adopted to challenge and counter the issues of extreme and harmful material online. Finally, leveraging new approaches from public health (Su et al., 2021; Shortland et al., 2021), we outline the major ethical, practical, and theoretical issues that pervade technology-based efforts to tackle the issue of extreme and harmful material online.