["Journal of Law and Society, Volume 48, Issue 2, Page 137-157, June 2021. ", "\nAbstract\nThis article asks how terrorism expertise has been mobilized in recent trials on terrorism financing. How is expert knowledge concerning ongoing and complex political situations involving alleged terrorism translated into factual evidence before a court of law? What kind of sources do courts use in terrorism cases, and what kind of expert knowledge is acknowledged or ignored? Through analysis of concrete cases under the United Kingdom (UK) Terrorism Act (2000) and the Dutch penal law Article 421Sr, we show how contested terrorism expertise becomes ‘certified knowledge’ that holds together as grounds for conviction before a court of law. This article contributes to socio‐legal debates on legal knowledge in two ways. First, we analyse the everyday, material practices of gathering, presenting, and contesting expertise in relation to security. Second, the article analyses new case material and a particular kind of knowledge – namely, security knowledge and terrorism expertise – to identify patterns in what is deemed relevant for the court.\n"]