The book provides analysis of the principal rules of trust law which control the exercise of powers and discretions by trustees. The primary focus is on the principle known as "the Rule in Re Hastings-Bass," and this is considered alongside the doctrines of fraud on a power and mistake. This is the first book-length treatment focused on this specific aspect of trust law, and in particular the first on the Rule in Re Hastings-Bass, which is the subject of much professional and academic interest especially following consideration by the Supreme Court in Pitt v Holt and Futter v Futter 2013]...