This paper proposes that diplomatic protection currently plays a prominent role in the establishment of State Responsibility derived from disputes involving foreign investors. Following a general introduction on the practical relevance of scholarly works on diplomatic protection in the field of International Investment Law, this article studies, firstly (I), the legal framework of diplomatic protection in the case law of International Courts (A) and the rules provided to that effect by Public International Law (B). On that basis, the article, secondly (II ), seeks to illustrate the legal challenges posed by diplomatic protection in a context where the subject is mostly regulated by International Investment Agreements. For that purpose, on the one hand, the solutions provided by the IIA s signed and ratified by Colombia are studied (A). On the other hand, practical consequences of such normative regulations are inferred upon in relation with international investment disputes (B). Finally the article presents conclusions on the topic through a brief remark on the attitude that, in relation to diplomatic protection, States should assume when an International investment dispute emerges.