This guidance document is a response to an internationally recognized need for additional instruction on the development of rules specific to a category of products for making claims based on a life cycle assessment (LCA). The purpose is to supplement existing standards for LCA-based claims that require the development of product category rules (PCRs) or their equivalents. The aim is that PCRs can be developed in a consistent manner and used to support claims based on multiple standards. The scope of the Guidance is global. The Guidance embodies the efforts of individuals with expertise in LCA and LCA-based product claims from more over 40 organizations in 13 countries and regions under the name of The Product Category Rule Guidance Development Initiative. The Initiative received no financial support from any standard or other product claim program and this Guidance reflects no bias toward any particular standard or program. The Guidance is intended to be a living document and we hope that it will continue to improve as the application of product claims based on LCA expands and diversifies.