This paper presents a pattern language with the objective to design, implement and maintain interdependent IT-systems from different vendors in the business context (so called ERP-Landscapes). They share the need to cope with heterogeneity. Heterogeneity in ERP-Landscapes has been induced by the ongoing specialization of applications in the business context (applications specializing in diverse fields like personal accounting, legal consolidation, inventory management, cost accounting and controlling). Sooner or later every business application has to interface with the input or output of other applications. From that moment you have to deal with the problems associated with an ERP-Landscape. Considering such a setting at design time will improve the adaptability of your applications. This paper characterizes different issues, which have to be considered when developing business applications in the context of an ERP-Landscape. The pattern language reflects a holistic approach showing the need to integrate both business and IT domain knowledge. Emphasizing on one aspect will decrease the over-all quality of the solution.