The purpose of this thesis is to understand testing as an inter-firm activity system focusing on collaboration (relationships, learning and knowledge sharing), quality measures (communication), innovation (co-creation of value), it highlights on why most studies treat testing as simply a structured technical process (single firm) and ignoring the inter-personal and inter-firm aspects. This research is about creating a more informed and sophisticated construction of the phenomenon of value creation in customer-supplier (inter-firm) relationships with emphasis to cosmetics and toiletries manufacturing and testing using activity system of the 3Cs: Collaboration; Communication; and Co-creation of values. This research shows, traditionally that learning has focused on single firm learning, paying attention to learning within focal firms. Firms learning today are more often done in inter-firm contexts. Companies of today are increasing their collaboration activities by taking part in inter-firm projects or temporary firms. This thesis has highlighted the need for better understanding of testing in inter-firm learning in those contexts. The thesisâs ambition is to develop further the concepts of firms learning where the context is inter-firm. Theoretically focus is on co-creation of value using the behavioral and cognitive process as a collective development. Through an intensive study, value is co-created through interactions in business relationships; it also identifies the area of collaboration, how value is co-created and the respective co-created value. Focus is also on how information is generated, interpreted and understood by participants across the learning projects, the test process, the agreement process, and what type of learning happens in an inter-firm activity system. The empirical parts are based on forty qualitative interviews and over 70 hours observations. This is based on three in-depth case studies (manufacturing/business relationships) drawn from the UK sector. Theoretically, the investigation is grounded using the Activity theory approach.