Executive summaries are one-page documents at the beginnings of longer reports that contain three or four parts: a description of the entity making the proposal (if this is pertinent to the report), a definition of the problem, the report's purpose and a summary of the report. The font and other visible formatting should match the rest of the report.
Executive summaries are typically written to synopsize persuasive documents like proposals or business plans. Because many busy reviewers will reject such plans based on the first page, it is critical that the executive summary be well-written and complete, with an eye to ensuring the reviewer reads the rest of the report.
The first paragraph should be treated as a "hook," a way to get the reader to continue. This might be talking about the proposing company so that it's clear the business is better able than others to solve the problem, or it might define a problem others have not yet identified. In any case, it needs to be interesting and clear. The solution to the problem should be included in the next section, with a special eye to how the authors of the proposal are especially qualified to address it. The last section of the report should be devoted to summarizing the problem, focusing on bringing a sense of urgency to solving it now.