This volume brings together trends and their prospects to understand the complexity of metacognitive phenomena, with emphasis on the interactions of metacognition with affect. It discusses the three perspectives in understanding these interactions: the possible mechanisms underlying them, the manifestation of interactions of metacognition with affect in self- and co-regulation in social and educational contexts, and changes during development in young children and older adults. This volume is a tribute to Professor Emerita Anastasia Efklides, who was among the pioneers to investigate and argue the importance of the interactions between metacognition and affect. It serves as a dedication to her contribution in the widening of the scope of research in metacognition and self-regulated learning.