This unit presents a current and modern overview of water and wastewater engineering with a focus on the treatment and reuse in a broad environmental context. The fields of water and wastewater engineering have evolved more recently into a modern field of engineering following important advances in the technologies used in primary disciplines such as environmental chemistry and microbiology. In particular, major advances/changes have occurred with respect to (1) the characterisation of constituents found in wastewater, both in terms of range and detection limits; (2) a greater fundamental understanding of the mechanisms of biological wastewater treatment; (3) the application of advanced treatment methods for the removal of specific constituents; (4) the increased emphasis on the management of biosolids resulting from the treatment of wastewater; and (5) the issuance of more comprehensive and restrictive permit requirements for the discharge and reuse of treated wastewater.