Online gambling is a profitable industry both in the regulated market and in the unregulated offshore market. Difficulties in regulating the offshore online markets are exacerbated by concerns over lacking consumer protection measures in offshore environments and reduced financial and tax revenue from gambling. Blocking is a measure employed by numerous regulators to prevent access or financial transactions to unregulated gambling sites. Yet, little is known about how well such strategies work. The current scoping review focuses on evidence on the effectiveness of blocking measures. Based on the review, 14 publications were identified. The analysis focused on four themes: implementation, effectiveness, risks, and alternatives. Results show that there is a paucity of empirical research on the effectiveness of blocking measures. The scarce evidence suggests that the effectiveness of blocking measures depends on implementation. Blocking without proper implementation may be an insufficient and disproportionate tool. The effectiveness of blocking is particularly limited by a constant need for updates in terms of technology and blocklists. We argue that research on and the effectiveness of blocking measures is obstructed by an asymmetry in expertise in three dimensions: Between regulators and industry; between ordinary and heavy gamblers; and between gambling and IT researchers.