This book is composed of selected papers presented at IWIFSGN'2019-The Eighteenth International Workshop on Intuitionistic Fuzzy Sets and Generalized Nets-held on October 24-25, 2019, in Warsaw, Poland, which is one of the main conferences on fuzzy logic, notably on extensions of the traditional fuzzy sets, in particular on the intuitionistic fuzzy sets. A considerable part of the conference sessions is also concerned with recent developments and challenges in the theory and applications of other topics exemplified by uncertainty, incompleteness and imprecision modeling, the Generalized Nets (GNs), a powerful extension of the traditional Petri net paradigm, and the InterCriteria Analysis, a new method for the feature selection and analyses in multicriteria and multiattribute decision-making problems. Some more general problems of computational and artificial intelligence, exemplified by evolutionary computations, machine learning, etc., are also dealt with. The papers included yielda good perspective on all of these important issues and problems.