This manuscript is composed of 18 contributions studying interactions in complex systems. These contributions were presented at the international conference on Interactions in Complex Systems, organized at University of Orléans in June 2013. This multidisciplinary manuscript aims at presenting how different disciplines may see their research topic from the complex system perspective and how interactions are accounted for in these complex systems. In this manuscript, we find contributions in mathematics, physics, computer sciences, robotics, life sciences, economics, linguistic, humanities or science of educationThe book is split into 4 parts, each one approaching interactions in complex systems from a particular perspective. We have gathered contributions by approach rather than by studied topic, the latter way being, to our viewpoint, less relevant to this type of book. The first part of the book contains papers dealing with interactions at the system level. The included contributions address territory planning, the traveling of population in the Neolithic era or interactions in neuron populations.The second part collects articles studying \textbf{networks} and proposing different methods for their analysis. This part contains contributions on link prediction, on interaction analysis in communities learning, on the influence of the type of strategies updates (parallel or sequential) on the evolution of cooperation among humans, opinion dynamics or the social function of gossip. Articles included in the third part focus on the analysis of interactions in social communications. As such, this part gathers papers studying teacher-student relations, the modeling of the teacher's evaluative speech to study students' interactions and the effects on learning or the modeling of human communications. Finally, the last part of this book is devoted to the analysis of interactions between economic agents in different fields. Thereby, a contribution develops a methodology to forecast employability of students in Earth Sciences; another article studies the importance of language and interactions between individuals as determinants of market equilibria; a mathematical model is derived to model money asset exchanges in the framework of a complex socioeconomic model in the third article and the last contribution of this part examines the study choice in an evolutionary game and show under which conditions the population of students splits into two classes of strategies in equilibrium