This article considers whether an investment bank, when acting as underwriter of a public securities offering, owes the issuing company the fiduciary obligation to avoid conflicts of interest. The question under Anglo-Australian law has not previously received judicial, scholarly or regulatory attention. The highly lucrative and visible nature of underwriting work creates powerful incentives for investment banks to accept instructions in the face of this duty. At the same time, the web of loyalties that these institutions owe, by virtue of their broad and diverse range of products and services, creates intractable practical difficulties for compliance with the duty. The article considers the factual nature of the relationship between a securities underwriter and an issuing company, the circumstances in which fiduciary obligations will exist outside the established fiduciary categories, and the existence, content and scope of any fiduciary obligation to avoid conflicts that arises. It also examines the practical and regulatory consequences for firms of the existence of this obligation.