Software development work undertaken by virtual teams dispersed across time, space, and organizational boundaries is referred as Global Software Development (GSD) with emphasis on “globalization”. In GSD, teams within same organization (off-shore) or different organizations (outsource) from multiple geographic locations are involved. GSD is becoming a norm and more software projects are undertaken in GSD setting due to the benefits associated with it. However, there remain many challenges that can adversely affect the ability to realize those benefits. One of the challenges is to overcome the problems faced during integration of the functional components developed by different teams at different geographic locations. Incompatibilities and hidden issues surface during functional components integration which is very costly to fix at this stage and can lead to delay, lower product quality or even failure of a GSD project. In this regard, this study investigates integration problems that occurred due to different reasons during different phases/stages of GSD, along with successful integration practices with their relative importance. The study produces lists of failure and success factors, and then further prioritized that failure and success factors lists through Delphi experts. Failure and success factors present an extensive knowledge of integration problems and practical solutions. In addition, their relative importance highlights the severity and importance of each failure and success factor. The results of this study not only help to understand integration issues and solution, but provide a platform to develop a solid strategy at early stage of GSD.