Can mailbox companies invoke the protection of investment agreements and sue in international arbitration courts? This work examines the protection of shell companies under the ICSID Convention, the North American Free Trade Agreement (NAFTA), and the Energy Charter Treaty (ECT). The results are nuanced: NAFTA and the ECT initially cover all shell companies; however, by analogy to the treaty provisions, contracting states can deny protection under the treaty to shell companies that are owned or controlled by nationals of the host state. According to the ICSID Convention, shell companies under 'host state control' are not considered eligible investors from the outset.