Investor-State arbitration is currently a much-debated topic, both within the legal community and in the public at large. In Towards Consistency in International Investment Jurisprudence, Katharina Diel-Gligor addresses the alleged proliferation of inconsistent decision-making in this field – one of the main points of concern raised in the ongoing discussions. After exploring whether such criticism is appropriate at all, she goes on to examine the different causes, forms, and manifestations of the inconsistencies that exist through a detailed analysis of ICSID arbitration. The author then canvasses possible approaches to reform and concludes that an ICSID preliminary ruling system – the practicalities of which are set out in the study – is a suitable means for enhancing consistency in investment arbitration and moving towards a jurisprudence constante.