This document discusses key aspects of cost estimating for construction projects. It begins by explaining that cost estimating involves both art and science, as it requires calculating costs based on data but also envisioning how a project will be built. The document then defines what an estimate is, the purpose of estimating, and the role of the estimator. It describes the skills required of an estimator and the typical components of an estimate, including materials, labor, equipment, overhead and profit. Finally, it outlines possible sources of error in cost estimates.