This module provides students with a strong foundation in biological principles for environmental engineering, with primary focus on natural biological processes. After an overview of biological principles and classification, the module reviews metabolic adaptations to various natural environments, including extreme habitats. Aspects of genetic adaptation and tolerance to environmental contamination are covered, together with the manipulation of biological processes to degrade and stabilise contaminants. Emphasis is placed on biodegration of organic pollutants and their bioremediation. Aspects of organic waste stabilisation and remediation of inorganic wastes are included. Lastly, the use of macrophytes for phytoremediation of contaminated soils is examined.