Here, we provide you with the preprint and with supplemental material (R-Codes) to the manuscript "Explaining the Longitudinal Interplay of Personality and Social Relationships in the Laboratory and in the Field: The PILS and the CONNECT Study" by Geukes, Breil, Küfner, Hutteman, Nestler, & Back (under Review). If you like to get in contact with us, please write an email to katharina.geukes@wwu.deAbstract:Our personalities (who we are) influence our social relationships (how we relate to the people around us), and our social relationships influence our personalities. However, little is known about the specific processes underlying the complex interplay of personality and social relationships. According to the PERSOC framework, the identification of underlying social interaction processes promotes the understanding of how personality and social relationships (a) are expressed, (b) develop, and (c) influence each other over time. The aim of the present paper is twofold: First, we outline four methodological challenges that arise when we empirically realize a process approach to the personality-relationship interplay. Second, we describe two empirical studies, that is, a laboratory-based process approach (Personality Interaction Laboratory Study; PILS) and a field-based process approach (CONNECT), both designed to meet these challenges. We provide detailed information about the samples (two student samples; PILS: N = 311; CONNECT: N = 131), procedures (longitudinal and multimethodological), and measures (personality and social relationships, appearance and behavior, interpersonal perceptions). For all these measures, we present descriptive information, reliabilities, and intercorrelations. In addition, we illustrate how these unique data sets can be applied to provide detailed process insights to answer topical research questions at the levels of the individual, dyad, and social network. We summarize how these studies meet the introduced methodological challenges, discuss the advantages and limitations of laboratory- and field-based process approaches, and call for their combination. We close by outlining an open research policy, aimed at collaborative and accelerated efforts to further open the process black box and ultimately leading to a better understanding of the expression, development, and complex interplay of personality and social relationships.