The Business Environment Sole Proprietorship .a business form for which there is one owner This single owner has unlimited liability for all debts of the firm Oldest form of business organization n Business income is accounted for on your personal income tax form 2-42-4 The Business Environment Oldest form of business organization. Business income is accounted for on your personal income tax form. Sole Proprietorship -- A business form for which there is one owner. This single owner has unlimited liability for all debts of the firm