Research in the field of information security economics has clarified how attacker and defender incentives affect cybersecurity. It has also highlighted the role of intermediaries in strengthening cybersecurity. Intermediaries are organizations and firms that provide the Internet’s infrastructure and platforms. This dissertation looks at how intermediary behavior and incentives can be understood from measurements—such as incident data and network logs. The question is answered through a literature review, four empirical studies, and two reflection chapters. The studies researched the role of ISPs in mitigating botnets, the success of anti-botnet initiatives in Conficker cleanup, vulnerabilities in the certificate authority ecosystem, and ISP incentives to deploy deep packet inspection, all using cross-country and longitudinal measurements. The dissertation concludes by reflecting on both the methodology and the broader implications for cybersecurity policy.