In a time of increasing awareness on environmental pollution and scarcity of natural resources, the term sustainability gained importance. This fact led to the evolution of methods and tools to account for consequences on the environment caused by products, services and new technologies developed, provided, and used by human being to, in succession, reduce the negative effects on our environmental system, now and in the future. Life cycle assessment (LCA) is one of a compilation of methods developed to investigate the environmental impacts, by taking into account comprehensive environmental information on the whole life cycle of product systems. This work, which is split into three parts, is focused on highlighting the best practices as also related issues that may emerge when conducting the life cycle assessment tool, in order to determine environmental burdens of complex systems. Complex in these terms is used to describe modeling of future related systems, including processes that are in an early stage of implementation, where system data is scarce, and where environmental impacts and mechanisms of certain processes are not yet entirely understood. It is feared that the validity of the current LCA procedure can be overrated, if applied beyond its limits. The first part of this thesis provides an insight into the characteristics, terms and procedures of the LCA tool, based on literature and the references of the International Organization for Standardization. Because of their international acceptance, the compilation of the 14040 series of ISO standards is employed as a basis for this work at hand. The second part comprises a research on selected case studies, related to the application of the LCA method in the area of complex system evaluation. An electricity generation system utilizing carbon capture and storage provides the addressed complexity to illustrate the requested practices as also the possible issues and limits of the LCA method. The third part constitutes an analysis on the examined LCA studies, emphasizing the basic practices but also the most relevant issues where the LCA method is seemingly stretched to its limit, which is presumably the circumstance if applied to complex systems. Additionally another example of a complex system, probably facing similar issues, is introduced, to confirm the relevance of emphasized aspects that might be subject for upcoming LCA improvement efforts. This example system then relates to the topic of energy storage, the utilization of the power-to-gas technology and underground hydrogen storage.