The prediction of future disasters drives the priorities, urgencies, and perceived adequacies of disaster management, public policy, and government funding. Disasters always arise from some fundamental dysequilibrium between hazards in the environment and the vulnerabilities of human communities. Understanding the major factors that will tend to produce hazards and vulnerabilities in the future plays a key role in disaster risk assessment. The factors tending to produce hazards in the 21st Century include population growth, environmental degradation, infectious agents (including biological warfare agents), hazardous materials (industrial chemicals, chemical warfare agents, nuclear materials, and hazardous waste), economic imbalance (usually within countries), and cultural tribalism. The factors tending to generate vulnerabilities to hazardous events include population growth, aging populations, poverty, maldistribution of populations to disaster-prone areas, urbanization, marginalization of populations to informal settlements within urban areas, and structural vulnerability. An increasing global interconnectedness also will bring hazards and vulnerabilities together in unique ways to produce familiar disasters in unfamiliar forms and unfamiliar disasters in forms not yet imagined. Despite concerns about novel disasters, many of the disasters common today also will be common tomorrow. The risk of any given disaster is modifiable through its manageability. Effective disaster management has the potential to counter many of the factors tending to produce future hazards and vulnerabilities. Hazard mitigation and vulnerability reduction based on a clear understanding of the complex causal chains that comprise disasters will be critical in the complex world of the 21st Century.