A sole proprietorship, also known as a sole tradership, individual entrepreneurship or proprietorship, is a type of enterprise owned and run by only one person and in which there is no legal distinction between the owner and the business entity. A sole trader does not necessarily work alone and may employ other people.

The sole trader receives all profits (subject to taxation specific to the business) and has unlimited responsibility for all losses and debts. Every asset of the business is owned by the proprietor, and all debts of the business are that of the proprietor; the business is not a separate legal entity. The arrangement is a "sole" proprietorship in contrast with a partnership, which has at least two owners.

Sole proprietors may use a trade name or business name other than their legal name. They may have to trademark their business name legally if it differs from their own legal name, with the process varying depending upon country of residence.

Registration of a business name for a sole proprietor is not mandatory in many countries, and is generally uncomplicated, unless it involves the selection of a name that is fictitious, or assumed. In many countries, the business owner is required to register with the appropriate local authorities, who will determine that the name submitted is not duplicated by another business entity.

The owner may hire employees and enlist the services of independent consultants. Although an employee or consultant may be requested by the owner to complete a specific project, or participate in the company's decision-making process, their contribution to the project or decision is considered a recommendation under the law. Under the legal doctrine respondeat superior (Latin: "let the master answer"), the legal liability for any business decision arising from such a contribution remains upon the owner and cannot be renounced or apportioned.

This is transposed by the unlimited liability attached to a sole proprietary business. The owner carries the financial responsibility for all debts and/or losses suffered by the business, to the extent of using personal or other assets to discharge any outstanding liabilities. Thus, the owner of a sole proprietorship may be forced to use his/her personal holdings, such as his/her car, to pay the debts. The owner is exclusively liable for all business activities conducted by the sole proprietorship and, accordingly, entitled to full control and all earnings associated with it.

In the Netherlands, a sole trader can be categorized as a "ZZPer", and must register with the Chamber of Commerce and get a VAT ID. Not all ZZPers are sole traders. A ZZPer (meaning Zelfstandige Zonder Personeel or self-employed without staff) is an entrepreneur who does not employ any staff to run their business. A business can be a sole proprietorship and also employ staff in which case the entrepreneur does not qualify as a ZZPer.

In Ireland, a sole trader who wishes to trade using a business name other than their true surname must register that name with the Companies Registration Office (CRO).