Investment screening mechanisms (“ISMs”) have been in a state of flux, both in practice and design, with a notable recent increase in new regulatory frameworks and significant amendments to existing screening systems that can be observed globally. Trust, or the lack of it, has been at the heart of the recent cluster of state activity related to ISMs. Accepting foreign investment proposals, especially in critical sectors and/or involving state-controlled entities, naturally increases the host state’s potential vulnerability and thus requires a higher level of trust toward both the investor and its governing home state. ISMs are therefore a manifestation of mistrust in their legislative form and a test of trust in their individual decisions. Despite being elusive empirically, as a distinct concept in international relations (“IR”) theory, trust is multidimensional in its abstract form and defies being easily captured within a singular definition. Nonetheless, taking this contribution poses two key questions. First, within the prominent schools of thought that provide alternative explanations of the concept in IR theory, how can we define trust and identify its role in foreign investment policy for the purpose of ISMs? Second, what are the appropriate legal tools that may be adopted to either build trust itself or at least to help mitigate the security threats that inward foreign investment may entail thus allowing for investment flows to safely continue despite the general presence of mistrust?