Cumulative risk refers to the combined threats from exposure via all relevant routes to multiple stressors incl. biological, chemical, physical, & psycho-social entities. Cumulative risk assessment (CRA) is a tool for organizing & analyzing info. to examine, characterize, & quantify the combined adverse effects on human health or ecologic resources from multiple environ. stressors. Essays in this vol. include: (1) If CRA Is the Answer, What Is the Question?; (2) A Phased Approach for Assessing Combined Effects from Multiple Stressors; (3) Vulnerability as a Function of Individual & Group Resources in CRA; (4) Assessing Cumulative Health Risks from Exposure to Environmental Mixtures -- Three Fundamental Questions; & (5) Using Biomarkers to Inform CRA.