This user's manual is designed to guide a user through the use of the software EPA PMF 1.1 for a receptor modeling application. The manual covers details about what the user should do to operate the software, but it intentionally does not include guidance on how to interpret the output, other than to provide indicators about how well the model fits the user-provided data. This manual is divided into 6 sections. The first section, this one, contains information about the development of the software and the model underlying the software. Section 2 describes the steps for installing, removing, or reinstalling the software from a computer system and offers important data management suggestions. Section 3 provides details about executing the software and Section 4 covers the output generated by the software. Section 5 covers some of the more advanced options, and the manual closes with a listing of numerous publications using PMF in Section 6.