We identify 33 areas where assurance services other than financial statement audits are currently offered or are emerging and conduct an extensive web search to document the contextual features of the services in each area. Using a framework for the expansion of assurance services, we analyze these features by asking: (1) Does the subject matter relate to financial information or controls? (2) Are criteria available to evaluate the subject matter? The answers allow us to categorize each area based on whether it represents an expansion opportunity to a traditional, but hypothetical, CPA firm. We then compare our expectations against observed areas where real-world firms have a presence. Finally, we report on two roundtables with senior assurance leaders to validate our findings and enhance our understanding of what is needed for each area to become, or continue to be, well-positioned for expansion by CPA firms.