It is widely accepted that thermally induced grain boundary chromium depletion in austenitic alloys such as austenitic stainless steels and Ni base alloys can lead to inter-granular stress corrosion cracking (IGSCC) of high temperature components during service. Numerous experimental studies of the phenomenon have been reported and many models have been developed to predict chromium depletion under different pre-service treatment. However, there are debates on some fundamental issues in modelling and the interpretation of experimental observations. This article attempts to clarify some of the issues through numerical calculations and examination of the literature on grain boundary chromium depletion.