Biological remediation including bioremediation and phytoremediation has been used to remediate contaminated sites due to their cost-effectiveness, energy conservation, and environmental friendliness. There are 24 articles in Critical Reviews in Environmental Science and Technology (CREST) from 2018 to 2022 focusing on this topic. Bioremediation employs microorganisms to modify and/or degrade contaminants, while phytoremediation uses plants to remove, contain, and/or change contaminants. They cover different contaminants including traditional (nutrients, petroleum hydrocarbons, organo-pesticides, plastics, and heavy metals such as Cd, Cr, Pb and U) and emerging contaminants (pharmaceutical and personal care products, and perfluoroalkyl and polyfluoroalkyl substances). However, these remediation technologies have limitations in applications including lengthy periods, environmental sensitivity, nutrient deficiency and contaminant toxicity. Therefore, improvement strategies including immobilization of microbial/microalgal cells, construction of microbial/microalgal consortia, and use of amendments have been employed to overcome its drawbacks. Further studies should focus on cost-effective strategies to enhance the efficiency of biological remediation and their environmental adaptability, especially under extreme environments and with emerging contaminants. Microbes, microalgae and plants with good contaminant removal capability should be coupled with engineering practices based on their interactive mechanisms among bio-association and contaminants at molecular levels.