Public interest in internet safety has grown alongside the proliferation of troubling content on social media platforms. The Online Harms White Paper, published in 2019 by the UK government, seeks to regulate an array of problems faced by internet users under the remit of online harms, grouping together both legal and illegal harms such as terrorism, child pornography, addictive content, and disinformation, to name but a few. This paper advances a greater understanding of the field of online harms policy in the UK, situating it within a broader history of internet discourse as well as future sites of debate. By employing two analytical tools, discursive institutionalism and the advocacy coalition framework, the paper elaborates on these theories in context of a new policy field and demonstrates the key actors and ideas surrounding the white paper. The government has framed online harms as an aggregated issue in order to propel a more protection-oriented logic of the internet that diverges from its more libertarian beginnings. The contestation that has erupted in response to the proposal illustrates two further strands of analysis. From the perspective of coalitions, it is found that mobilisation patterns in a new policy field reflect the differential resources and motivations of coalitions, resulting in more activity by proponent coalitions and less by opponent coalitions. From the perspective of discourse, contestation over the white paper highlights long-running concerns in internet policy, and concurrently shapes the emerging debate in the new field.