Integrating a behavioral science lens into the World Bank projects can enable staff to create meaningful, efficient change without relying on the kinds of traditional tools that can take years to implement. As Marco Hernandez, described, in Guatemala, where improving tax compliance can take years and often requires building institutional capacity and strengthening systems, behavioral science provided a new way of increasing payments. Letters to non-compliant tax payers with behavioral messages integrated—including those incorporating social norms, and intentional choice—were incredibly effective in increasing compliance at low cost. Recipients of the letters ended up paying four times as much in taxes compared to those in the control group.