An executive summary is a portion of a business plan that sums up all of the information a business plan contains. Since this is a summary of the plan's contents, you write this piece last. For a start-up business, you might be writing a business plan and executive summary to present to a lender for financing. It provides the lender with a preview of what the plan details. According to the website Bplans, the executive summary includes five primary parts: the business name, the business location, the product or service you sell, the purpose of the business plan and projected sales and profits.