Federal and state regulatory agencies that are concerned with issues of environmental management have adopted approaches toward policy-making that are dose- and risk-informed. To that end they (and others) have developed environmental models and computer codes to mimic the transport of contaminants along air, water, food-chain, and related pathways for estimating potential exposures, doses, and risks to individuals, populations, and ecosystems. Their calculations commonly find application in the planning of remediation, and thereafter in the demonstration of compliance with federal and state cleanup standards. As the models and codes have become more sophisticated, so also have requirements on the accuracy and level of detail of the numerical point values and probability distributions of environmental transfer factors and other parameters that serve as input parameters to them. In response to this growing need, the federal Interagency Steering Committee On Radiation Standards (ISCORS) and the Argonne National Laboratory have developed an on-line, national repository of information on parameter values and distributions of known provenance and demonstrated utility. The ISCORS Catalog of References to Parameter Values and Distributions Used in Environmental Pathway Modeling for Cleanup of Sites Contaminated with Radioactivity is a web-based, indexed compilation of references, compendia, databases, and other sources of peer-reviewed information on parameters. It does not itself contain numerical point values or distributions for any particular parameter, but rather it provides links or directions to sites or other published materials where such information can be obtained. Designed to be user-friendly, easily searchable, and readily up-dateable, the Catalog is being filled, after some initial priming, mainly through on-line submissions of proposed references by the Catalog users themselves. The relevant information on a proposed reference is submitted to ISCORS in a simple, standardized format; it is vetted (with acceptance criteria such as publication in a peer-reviewed technical journal, or appearance in a formally-issued federal agency report) and then added semi-automatically to the Catalog. Built around a relational database, the system offers subject- and text-search capabilities, provides information on parameter definitions and methods of measurement, on transport/exposure pathways, and on standard models and codes. The Catalog is intended for use by (and being populated by) the professionals, managers, and others involved or interested in the application of pathway modeling to estimate doses and risks associated with sites contaminated with radioactive or other hazardous materials.