This article examines the scope and the limits of icsid arbitration involving umbrella or “observance of undertakings” clauses and widely-formulated arbitration clauses, both of which may provide investors with broad recourse to dispute settlement for disputes related to investment, as defined in the applicable bilateral investment treaty (bit). It does so by analysing the origins and rationale behind both clauses as well as how they operate in principle and in practice. It appears there is no jurisprudence constante concerning the application of either clause. However, a clearer picture is emerging in icsid jurisprudence of an effective, occasionally prospective, application of the umbrella clause and some limited deference to widely-formulated arbitration clauses. It is balanced by other icsid arbitral decisions that seek to limit the scope and application of the umbrella clause on a variety of grounds.