Outsourcing any activities generates relationships between the buying and selling companies that need to be well managed to ensure that a positive effect comes from said relationships (Roth and Menor, 2003). In the particular case of logistics activity there are many companies that forge long-term links with specialized suppliers in order to increase benefits and decrease risks in logistics outsourcing, improve efficiency and profitability, and offer a better customer service performance (Krizman, 2009). The success of these relationships and, by extension, of the outsourcing of the logistics activity, can become important for achieving a competitive advantage (Fawcett and Cooper, 1998). However, customer company – logistics services provider relationship design and management during the interaction (herein referred to as interaction interface) have been considered to be at the root of the wide differences found in the results of logistics outsourcing (Hartmann and de Grahl, 2012), as can be observed in a range of studies (e.g., Boyson et al., 1999; Lieb and Bentz, 2005; Gadde and Hulthen, 2009). Accordingly, it seems that it is essential for special attention to be given to the design and management of the interfaces of the interaction that determines the logistics outsourcing buyer-service provider relationships (Whipple and Roh, 2010; Hammervoll, 2009). A variety of authors state in relation to this that the design and management of these interfaces is a major determinant of the results that come from customer-provider relationships (e.g., Sampson, 2000; Hertz and Alfredsson, 2003) and that it is essential to know what aspects positively impact the results of outsourcing (Deepen et al., 2008). Despite the importance of the topic, empirical research in the field is limited (Wallenburg et al., 2010). In order to address this gap, the present paper focuses on the design of the interaction interface and its effects on the success of logistics outsourcing. This design establishes the organizational resources required from the buyer and the seller (van der Valk, 2008), among which human resources are especially relevant (Roth and Menor, 2003). In fact, the quality and productivity of outsourced services are often highly dependent on the human resources involved in the production, delivery and consumption of said services on both sides of the relationship (Grönroos, 2000). In line with the above, following Cunningham and Homse (1986), Wynstra et al. (2006) consider that there are two aspects of human resources that must be taken into account in interaction design, which together comprise what these authors call structural dimensions of interaction. These dimensions are the types of organizational resources of either party involved in the outsourcing and, more specifically:

• Representatives involved: type of functional representatives involved in ongoing interactions, both in the buying company and the service provider.

• Critical capabilities: skills that buyer and service provider representatives involved in the interaction should master.