In this chapter, Regulatory Toxicology of Pesticides: Concepts, the main topics summarised are the key processes of human health risk assessment of pesticidal active substances as well as plant protection products and biocidal products. Based on submission of various toxicity studies from the applicants and also consideration of the peer-reviewed literature, the hazards are identified, dose–response relationships are characterised and toxicological threshold values are derived. This is followed in the authorisation procedure by comparison of toxicological thresholds with the exposure data in the risk assessment. Future trends and new methodologies in regulatory toxicology will improve the risk assessment, including the consideration of metabolites, the development of test guidelines as well as cumulative risk assessment. Microorganisms used as pesticides also have to be given attention.