There are several that are guild-like. For instance, in my state it is illegal to hold yourself out as providing 'accounting services' without being a CPA. Like

There are several that are guild-like. For instance, in my state it is illegal to hold yourself out as providing 'accounting services' without being a CPA. Likewise, it is illegal to assist in the sale/purchase of real estate for a fee without being a broker/realtor (or a lawyer). It's undoubtedly the same for engineering. However, there may be a subtle difference... A non-accountant can certainly help with your books so long as they don't hold themselves out as an "accountant." And, a non-realtor can certainly help you find a house, so long as they aren't paid contingency related to the ultimate transaction. I think -- and I may be wrong -- a non-engineer can charge to design a treehouse for your... so long as he doesn't hold himself out as an engineer. (Obviously, when it comes to roads, permit-related structures, etc., a governmental agency may require a P.E.... but, that's a different set of requirements.) But, one may not practice medicine EVEN IF one refrains from holding himself out as a doctor. And, one may not dispense legal advice EVEN IF it is clear to all involved that the person is not a lawyer.