Purpose - The purpose of the bachelor thesis is to describe the relationship between Third-party logistics (3PL) suppliers and car assemblers under Just-in-sequence (JIS). The paper refers to a case in the Spanish automotive industry and the main target is to identify and analyse the potential problems between both parts and explain how they work together. Methodology – The paper is based on a case study research, with the aid of interviews with people of the industry and participant-observations, to explain how this part of the supply chain works, the relationships along the chain and the difficulties of sequencing. Results – The paper identifies and analyses the potential problems between both parts and relates how a mistake from one of them can affect the other one. Then, the results are discussed and associated with some concepts of the theoretical framework. Limitations - The results of this case study can only be related to the Spanish automotive industry, for car assemblers that work under a JIS context with several 3PL suppliers. The case study only identifies and analyses the problems, solutions and measures for managing them are not provided.