A sole proprietorship, or simply proprietorship, is a type of business entity which legally has no separate existence from its owner. Hence, the limitations of liability enjoyed by a corporation and limited liability partnerships do not apply to sole proprietors. All debts of the business are debts of the owner. It is a "sole" proprietor in the sense that the owner has no partners. A sole proprietorship essentially means a person does business in his or her own name and there is only one owner. A sole proprietorship is not a corporation; it does not pay corporate taxes, but rather the person who organized the business pays personal income taxes on the profits made, making accounting much simpler. A sole proprietorship need not worry about double taxation like a corporate entity would have to.

Most sole proprietors will register a trade name or "Doing Business As". This allows the proprietor to do business with a name other than his or her legal name and also allows the proprietor to open a business account with banking institutions.

In the United States self-employed workers are paid directly by clients or by their business, and some proportion of these payments will be due to the government as income tax.

In the United States, a person running a business as a sole proprietorship or a limited liability company is considered self-employed for tax purposes, but the sole shareholder of an S Corporation is not considered self-employed. Such a person is considered an employee of the corporation and does not pay self-employment tax, but instead pays FICA tax (matched by the corporation) at half the tax rate at which the self-employment tax is imposed -- 7.65% each by employer and corporation, instead of the 15.3% self-employment tax.