Problem: The developing business market and the pressure it puts on business gives rise to new fields of business within SCM and logistics. Third party logistics (TPL) services have grown rapidly in importance as an alternative to vertical business integration. The emergence of TPL has brought about interest in the topic by academia, but recent literature reviews express a need for research on TPL relationships where both buyer and provider perspectives are viewed simultaneously, since a majority of previous research has been conducted more from a single organisational viewpoint. Purpose: The purpose of this thesis is to investigate how providers and buyers in TPL relationships adapt and cooperate to develop mutually beneficial and long-term relationships, as well as investigating their willingness and attitudes in this concern. Method: The thesis combines an explanatory and exploratory classification, and performs a qualitative, mono method study of viewpoints on TPL relationships from Swedish and Norwegian providers and buyers that currently are in a TPL relationship. Semi-structured interviews are conducted with four providers and three buyers. The findings are analysed and interpreted in light of a theoretical framework developed from the literature review, which in the analysis is applied in a TPL context to extend the understanding of TPL relationships. Conclusions: Willingness to adapt and cooperate in TPL relationships is connected with the parties’ perceived potential for economic gain and also with being able to trust the other party. Buyers emphasise the need for providers to have knowledge about the buyers’ business. Providers emphasise the need for buyers to be knowledgeable about their own business and for the buyer to fits their solutions. Attitudes: Both parties emphasise communication as crucial for the development of mutual benefits. Buyers adapt to providers’ standards as far as possible. Providers seem to want buyers to adapt to their solutions to gain economies of scale, and therefore appear reluctant to make relationship-specific investments. The use of contracts in the TPL context appears to contradict literature in that contracts work as a foundation for building trust, as well as for reducing opportunistic and operational risk. In practice, both providers and buyers highlight the use of integrated IT-solutions as a means of adapting to each other. Regular operational meetings are emphasised as part of the practical cooperation to develop the relationship’s future and to discuss day-to-day issues.