IICRC R520-2015 is written for use by those involved in the mold remediation industry, primarily for mold remediation companies and workers, and secondarily, for others who investigate or assess mold complaints, prepare remediation specifications, protocols or procedures, and manage remediation projects, (e.g., indoor environmental professionals (IEPs), other specialized experts) and finally, for other potential materially interested parties (e.g., consumers and occupants, property owners and managers, insurance company representatives, government and regulatory bodies). The S520 is a procedural standard. It is based on reliable remediation principles, review of available scientific and industry literature and information and practical experience. In addition, there has been extensive consultation with, and information obtained from, numerous other sources. The Second Edition of the S520 has been updated and rewritten. An additional Chapter and Section have been added covering Building and Material Science, and an additional section has been added covering Equipment, Tools and Materials. This document supersedes the IICRC S520 Standard and Reference Guide for Professional Mold Remediation (S520 First Edition 2003, 2004 and 2008)." The ANSI/IICRC S520 Standard summarizes most of the significant and important procedures and methodologies of a mold remediation project, while the IICRC S520 Reference Guide restates and further explains those procedures and methodologies, and provides additional background information, which supports the Standard. Although the material in the Reference Guide does not carry the official status of a Standard, the two sections complement one another and should always be considered in tandem.