The combination of formal systems and algorithms, their logical and algebraic background, as well as the general architecture of complex and interacting systems has recently become a very active research area. The First International Workshop Frontiers of Combining Systems created a common forum for the different research activities on this topic in the fields of logic, computer science, and artificial intelligence. Its main intention was to stimulate an interdisciplinary discussion that focuses on different aspects of the combination problem. This volume contains research papers that cover the combination of logics, the combination of constraint-solving techniques and decision procedures, the combination of deductive systems, the integration of data structures into Constraint Logic Programming formalisms, and logic modelling of multi-agent systems. These problems are addressed on different conceptual levels: from the investigation of formal properties of combined systems using methods of logic and mathematics to the consideration of physical connections and communication languages relevant for combination of software tools.