The organizational socialization field has received considerable attention in both academic and popular writing. Accounts take either an organizational view - focusing on the socialization tactics organizations use to bring about desired change in the individuals they recruit - or a newcomer view - focusing on how individuals integrate successfully. The literature suggests that the mechanisms whereby both processes are achieved is carried out through social interaction. However, the nature of this relationship-building process lacks a clear conceptual and empirical underpinning. The principal objective of this thesis is to develop a framework explaining/suggesting how newcomers build relationships with others and how their personal networks change in early organizational socialization. Drawing on the socialization and social network literatures, the framework proposes a four stage framework - Newcomers' uncertainty in a new organization, Relationship initiation process, Relationship straightening and persistence over time and Newcomers' network change. Longitudinal empirical evidence, of forty newcomers' personal networks, suggests that self-monitoring, extraversion and protean career behaviour influence newcomers' selectivity in adding support providers in their personal network, however uncertainty is important only for predicting relationship building to get social support. Overall, newcomers need more informational than social support in the early organizational entry. Organizational socialization tactics explained the extent of social support received, but not the extent of informational support. Finally, the willingness of support provider to give help and similarity of support provider based on age determined which support provider was contacted. The thesis contributes to the organizational socialization literature by showing the selectivity of newcomers in building relationship in the early organizational entry. It shows the importance of socialization tactics and the perception of uncertainty newcomers perceive for the extent of support received. It also acknowledge the dyadic role of other socialization agents in the relationship building process. Lastly, the thesis also contributes to the social network literature by looking at the effect of individual differences and contextual variables in the personal network dynamics.