In this book, the authors discuss the ecology, biological implications and environmental impact of microcosms. Topics include using microcosms to investigate aspects of plant-bacterial interactions and bacterial evolution; multifactorial microcosm experiments to predict how plant species and assemblages respond to changes in the availability and spatio-temporal heterogeneity of resources like water, light and nutrients; development and optimisation of an aquatic laboratory microcosm for ecotoxicological risk assessment; assessment on transformation of organic pollutants in microcosms; bacterial evolution in simple microcosms; ecology and environmental side-effects of pesticides in tropical microcosms; floating dish microcosms to study the developments of biofilm communities; the role of semiosis and cohesion and sustainability inside microcosms; and soil microcosms and biogeographical research.