The project focuses on how we react as bystanders when exposed to online political hostility. The project hypothesizes that such bystander decision-making is shaped by:

• factors at the level of message content (ambiguity and severity of hostility), 
• bystander characteristics (partisanship; identification with victim or perpetrator), 
• situational circumstances (perceptions of responsibility, response efficacy and costs of reacting)
• online context (design of social media platform; encouragement of pro-social reactions).

Further, the project hypothesizes that pro-social bystander reactions to online political hostility may encourage bystander mobilization in the short run by lowering the costs of reacting and ambiguity of the situation and increasing a sense of responsibility and altering norms of apathy in the longer run. 

And that pro-social bystander reactions can be encouraged through interventions providing motivation and guidance on how to react to online hostility in a pro-social manner.