This article presents the situation of 'Missing Investment Treaties' (MITs), defined as those International Investment Agreements (IIAs) that have been concluded by States, but their texts (and in some cases their existence) are not publicly available or incomplete. In order to determine the number of MITs, we examined the text and language availability of IIAs concluded by countries, that are publicly available, and we complemented that information with country-specific searches from international, governmental and private sources. In turn, the article explores possible explanations to this State's behaviour, using the following questions as guidelines: Why would countries sign agreements that are supposedly negotiated to promote, protect or liberalise foreign investment without making those texts available? If a text of an IIA is publicly available, does it correspond to the language of both contracting parties, only one of them, or of a third country? Is it possible to achieve IIAs' objectives if the text of the treaty is not available, or is it available only in one language? Might there be other reasons to sign these agreements?