Top-Down Estimating is a project management technique where the overall project cost or duration is estimated first, based on historical data or expert judgment. This method provides a quick overview and helps in setting initial budgets and timelines, allowing for adjustments as more detailed information becomes available. In this approach, project managers break down the total estimate into smaller components later, refining the details as the project progresses. It is often used in conjunction with other estimating methods, such as Bottom-Up Estimating, to create a more comprehensive understanding of project requirements and resources.