CONTAMW is a general purpose, multi-zone (nodal) airflow and contaminant transport analysis tool that can be used to determine interzone pressure differences, airflow rates and contaminant transport in complex building structures. This tool was developed by the Building and Fire Research Laboratory of NIST for the analysis of building ventilation systems and has evolved and adapted to accommodate a wide range of building engineering disciplines from indoor air quality analysis to smoke management system design. This report serves two purposes: as a manual for implementing the most recent enhancements to the program and as documentation of the inner workings of the program. The documentation of the inner workings addresses both the graphical user interface (CONTAMW) and the numerical solver (CONTAMX) of version 2.1 of the program collectively referred to as CONTAMW.