Should you write the Executive Summary first and build your proposal to support it, or should you write it last, as a summary of all the material developed in writing the proposal? There are good reasons for taking either approach, but which is best for you will depend on your circumstances and goals.
Why You Should Write the Executive Summary First
Writing the Executive Summary first forces you to think through the most important aspects of your proposal. The purpose of a proposal is to persuade the reader to follow your recommendations. The Executive Summary succinctly presents your recommendations. The proposal must articulate and support the reasons that will persuade the reader. Writing the Executive Summary first forces you to articulate those reasons. If you just start writing the proposal and figure out why you are the customer's best alternative by writing about it, your proposal will miss many opportunities to be persuasive, and the reasons why the reader should follow your recommendations will never be fully integrated.
Writing the Executive Summary first forces you to articulate your reasons and develop the elements of persuasion. It then provides you with a foundation to build that rationale into the proposal, and enables you to achieve a fully integrated presentation.
Why You Should Write the Executive Summary Last
You learn a lot as you develop your proposal. On the last day of production, you know far more about what is required to win than you did on the first day. It is a tremendous challenge to gain this insight before it is too late. The Executive Summary that you can write on the last day will always be different from the Executive Summary you would write on the first day. If you build your proposal around what you know on the first day, you will be building your proposal around incomplete knowledge.
While you could argue that starting early and doing your intelligence gathering homework is the best way to respond, you will never have full knowledge at the beginning. This is true, if only because of the RFP. Going through the RFP, item by item, and developing your solution and your response teaches you things. The strategies that were developed before the RFP was released often need to be changed or even dropped based on what is in the final RFP. And even if you are really diligent about reading the full RFP as soon as it comes out, you won't have a full understanding of all the implications until you've fully developed your solution, written the response, and gone through all the related pricing trade-offs.
When you write the Executive Summary last, it will reflect a better understanding of the customer, the solution, and the competitive environment. As a result, it will be more persuasive.
How Do You Decide?
Like many things in life, the best approach for you will depend on your circumstances. If you are having trouble articulating why the customer should follow your recommendations, then doing the Executive Summary first may be an excellent way to start. You can always go back to it later and make changes. If, however, your rationale depends on what your recommendations are, and you won't know until they are developed and priced, you may wish to hold off. Only don't hold off too long or you will run out of time.
A hybrid approach is to create a draft Executive Summary, with a expectation that it will get thrown out or completely revised as you go through the process and learn more. What I like about this approach is that if you revise it as you go along, you have a baseline understanding of your rationale that you can share with people throughout the process to help foster a shared-understanding and illuminate any discrepancies. If you end up revising the Executive Summary on a daily basis, the effort is not wasted. Confirmation, validation, and revision of the reasons why your customer should follow your recommendations can only help you achieve a successful proposal.