<p>This dissertation posits that social media platforms (e.g., Twitter and Facebook) represent a new process and fora for the development and implementation of norms that regulate environmental behaviour, with unique characteristics, strengths, and weaknesses, when compared with conventional processes and fora for regulatory activity and codified norm development, such as state-based legislative assemblies and non-state standards bodies. Distinctive features of social media platforms affect user interactions and experiences, which in turn impact how environmental norm conversations take place on those platforms, as opposed to norm conversations that take place through legislatures or formal standards processes. In addition, distinctive characteristics of public sector, private sector, and civil society actors affect how they use social media in development of environmental norms. This research hypothesizes that the way in which social media is used to formulate environmental norms and the importance of social media as a venue for environmental norm conversations varies, depending in large part on distinctive characteristics of the governance actors (i.e., government, third sector actors, and the private sector) and their societal roles, interacting with the distinctive characteristics of social media. In addition to a cross-disciplinary review of scholarly literature, this dissertation explores the veracity of this hypothesis using two investigations; one that compares the use of Twitter by two Ontario government agencies, and a second case study that explores of a Twitter micronorm conversation about the groundwater operations of the water bottling industry in Ontario and other jurisdictions. </p>