This paper aims to develop a generally applicable model to examine the eventual motivations both for internal migration and external immigration. For this reason our model involves not only economic motivations of development and geographical economics but also social motivations of behavior economics. We tested the model through Turkish internal and external population flows toward German regions. Our analysis contains the first regional-level immigration analysis between an EU country (Germany) and Turkey. The main results are: (i) the purely economic motivations are more important than the social motivations; (ii) among the economic motivations income level and economic size of host regions are the biggest ones; and (iii) and the network externalities play a more important role than the herd effect. Subsequently, we estimated some country-specific factors on im/migration. The main results are: (i) joining to the Customs Union led to acceleration in intern migration but slowing-down in external immigration; (ii) even though Turkey acts slowly in adopting EU reforms, the EU reform process seems to reduce the economic and social stress on Turkish im/migration; and (iii) the reunification of Germany created a constraint on Turkish immigration flows toward German regions.