PEIRCE is an interactive relational database management system intended for mini and microcomputers, with an extensible command facility, QUERY, based on Codd's relational algebra and supporting a clerk oriented interface. PEIRCE contains three major independent on-line modules: DBA, QUERY, and CSU. DBA provides the data definition and data dictionary facilities and is discussed in Section 2. QUERY provides both a relational algebra data manipulation language and a clerk oriented interface. QUERY is also discussed in Section 2. Command sequences are discussed in Section 3. We discuss the virtual file facilities of PEIRCE (which include the updating of virtual files) in Section 4. The underlying storage structure, namely entry order sequence with secondary indexes, was chosen primarily with simplicity of recovery in mind and is discussed in section 5. In Section 6 we discuss the control commands IF and FOR, which help to conveniently avoid having a host language facility. We conclude in Section 7 by describing further work planned on PEIRCE.