The book presents the most important professional and scientific activities of the authors in the operation and planning of electric distribution systems from the last 10 years. These research directions were motivated by the current technological developments in the power engineering field and the gradual implementation of smart grids. At present, at European level, distribution systems have a high degree of automation of distribution, using industrial standards, so transition from the current situation to the smart grids concept is technically feasible. This concept was defined both in the industrial and academic environments take different forms by focusing attention on several particular issues: active consumers, distributed generation, active participation in the electricity market, etc. Each of these development directions is designed to respond to a part of issues regarding the smart system, similar to the pieces of a puzzle game. It is obvious that the ultimate success ofany initiative which refers at the transition to the smart grids concept is determined by the presence of the smart entity that consistently places the pieces of the game in a consistent manner.