This recommended practice (RP) addresses the processes required to successfully implement process control systems for refinery and petrochemical services. The major topics addressed are as follows. ?? The basic functions that a process control system may need to perform@ and recommended methodologies for determining the functional and integration requirements for a particular application. ?? Practices to select and design the installation for hardware and software required to meet the functional and integration requirements. ?? Project organization@ skills and management required to execute a process control project and then to own and operate a process control system. The first editions of API 554@ Part 2 and API 554@ Part 3 have been prepared by a collaborative effort of the API Subcommittee on Instrumentation and Control Systems and the Process Industries Practices (PIP) Process Control Function Team. As such@ the general scope of the material contained has been expanded to cover general industrial process control topics that are applicable to both refineries and petrochemical facilities (PIP is a consortium of owner and engineering/construction contractor companies whose purpose is to produce a set of harmonized engineering standards in a variety of discipline areas@ including process control). Although the scope has been extended beyond traditional refining services@ the user is cautioned to fully consider the requirements of the particular applications and circumstances that may exist and carefully apply the concepts described in this RP as appropriate. This document is not intended to present a tutorial on the subjects discussed@ but rather to aid the reader in identifying and understanding the basic concepts of process control systems. The references provided within the document direct the reader to publications that describe one or more subjects in greater detail than is necessary or desirable for the purposes of this document.