This guidance is intended to assist state, regional, and local environmental professionals in tracking the implementation of best management practices (BMPs) used to control agricultural nonpoint source pollution. Information is provided on methods for selecting sites for evaluation, sample size estimation, sampling, and results evaluation and presentation. The focus of the guidance is on the statistical approaches needed to properly collect and analyze data that are accurate and defensible. A properly designed BMP implementation monitoring program can save both time and money. This document provides guidance for sampling representative farms to yield summary statistics at a fraction of the cost of a comprehensive inventory.