Introductory remarks on the special issue of Optimization and Engineering dedicated to SDEWES 2021 conference

The background of this Special Issue (SI) of the Optimization and Engineering (OPTE) journal is the 2021 Sustainable Development of Energy, Water and Environment Systems (SDEWES) Conference. This broad field was discussed by the participants of the 16th SDEWES Conference held in Dubrovnik, Croatia. This SI aims to bring together articles that discuss recent advances in optimization methods and algorithms that integrate various life-supporting systems. A decision-making problem often appears as a parameter estimation problem; it can be formulated as an optimization model and solved using different optimization algorithms and techniques. All papers included in this OPTE journal SI consider aspects of numerical analysis, mathematical modelling, and computational methods involved in investigating, planning and implementing sustainable development. In this context, the guest editors have confidence that the selected papers and addressed issues will substantially contribute to the increase of the knowledge body published in the OPTE journal, and the SI will be a powerful platform for researchers to discuss, share, and disseminate new ideas.