A Practice Note considering the purpose, scope, and practical application of due diligence investigations in connection with SEC-registered securities offerings and unregistered securities offerings. It reviews the applicable federal securities law liability provisions and the due diligence defenses available to offering participants when an investor brings suit under federal securities antifraud provisions alleging a material misstatement or omission in the offering disclosure. It also identifies the differences among legal, business, financial, and accounting due diligence.