The term meromixis was introduced more than 80 years ago to denote lakes that do not annually mix completely. Since then our understanding of meromictic lakes has considerably advanced. Physical processes support the difference in water density between deep (monimolimnion ) and surface (mixolimnion ) waters in meromictic lakes; such lakes reveal complex biogeochemical interactions that contribute to the maintenance of meromixis. This Conclusion chapter of the book on Ecology of Meromictic Lakes presents the general overview of physical, chemical and biological properties of meromictic lakes, based partly on the foregoing 12 chapters. The broad spectrum of meromixis supported by different processes in lakes located in different regions and climates is presented. We stress the importance of undisturbed sediments in meromictic lakes as paleolimnological archives and demonstrate how this information can be used to reconstruct lake history and development over longer time periods. The effects of switch from holomictic to meromictic regime and vice versa on the food web and biological community are demonstrated by some of the case study lakes. However, we do not have the mathematical or modeling tools to understand all the causal factor for processes that switch the mixing regimes of lakes. Man-made meromictic lakes (pit lakes) can be used as lake management tools to control water quality in lakes . We discuss that numerical simulations and model forecasts are important tools to predict the mixing regimes in both man-made and natural meromictic lakes. Biogeochemical reactions play important role in cycling of nutrients in meromictic lakes. Both anoxygenic photosynthesis and chemolithoautotrophy are exceptionally important for fixation of inorganic carbon in organic matter in meromictic lakes. These carbon fixation activities link the carbon cycle with the sulphur, nitrogen and iron cycles. Studies of meromictic lakes—aquatic systems where physics, biogeochemistry and ecology interact intensively—give us new insights into the limnology of inland lakes.