The on-going enhancement of information sources and tools to augment the understanding of chemical toxicity in human and environmental systems is a critical aspect of systems toxicology. This chapter highlights multiple free on-line information sources and tools categorized into toxicity-related; chemical–gene–protein interactions; biological pathway–network relationships; chemistry, structural alert, and quantitative structure–activity relationships (QSAR)-related; and drug and drug-target information. These databases and tools represent the latest non-commercial sources for expanded research and safety assessment in toxicology research.