This article examines the requirement of the Nigerian Investment and Securities Act, 1999 (ISA) that securities be registered prior to being offered to the public, with a view to determining the limits (boundaries) of that requirement. It shows that the boundaries can be staked out along three dimensions: items excluded from the registration requirement because they are not caught by the definition of securities under the ISA; items that qualify as securities under the ISA's definition of that term but which are exempt from registration for various policy reasons (exempt securities); and items which are exempt only because of the nature of the transactions involved rather than the nature of the securities themselves (exempt transactions). It shows that while doubts about the limits of the registration requirement exist at some points where the boundaries cannot be readily staked out without interpretive difficulties, such doubts and the points in relation to which they exist are relatively residual, except in areas where the Nigerian Securities and Exchange Commission has in its rule-making manifested a misconception of its powers under the ISA.