If you're preparing a business plan for an existing business, you'll find the financial and operating information developed over the business's life to be absolutely essential. This historical information can provide much of what you need for a written business plan. Your business's track record of operations is probably memorialized in a number of ways. You keep books, keep customer and supplier information, file government documents, pay taxes, and perhaps even have some employees with payroll records and personnel files. If your recordkeeping efforts are even more sophisticated, then you may also have cash flow projections, spreadsheets, and other documents that contain information you can use in drafting a plan.