As Joseph Slater describes in his chapter in this volume, the most fundamental question in labor and employment law is whether an employment relationship exists. Currently, there are only two answers to that question – “yes” or “no” – the consequences of which are immense. A “no” means that the workers exist outside of our workplace regulatory scheme; they have no right to organize; no protections against retaliation; and no guarantees of safety, health, wages, and other rights enjoyed by statutory employees. But even when there is no issue about a statute’s jurisdiction over the workers and firms involved in a dispute, determining whether an employment relationship exists can still pose challenges. In particular, when multiple firms are involved in the supply or use of labor, it can be quite difficult, yet vitally important, to identify the responsible “employers.” Just like fundamental questions about a statute’s applicability to workers or firms, determining which firms are classified as employers is often the dispositive factor in whether workers are able to enjoy their statutory rights.