In this volume, both qualitative and quantitative scholars describe their findings on the networks of migrants and their descendants and explore the content of their social ties for educational and labor market success in seven European countries. Some contributions cover decades of work in this field, making this one of most comprehensive books on this topic, both theoretically and empirically. Almost without exception, the authors, although describing various ethnic groups, different geographical and professional contexts and different time periods, are critical of a number of the main arguments about the networks of migrants developed in the field of migration studies. Central in their critique is the question about the importance of co-ethnic or inter-ethnic ties and networks, and their importance to enter the labor market and move up. In the field of migration studies, concepts like integration and assimilation have greatly influenced the thinking of its scholars. The idea that newcomers only become fully integrated in a society when they gain a similar economic position and are in contact with people without migration background, or, in other words, become part of the mainstream, has been a strong and dominant view in our field (Alba & Nee, 2003; Alba, 2009; Portes & Rumbaut, 2001; Portes & Zhou, 1993). People who largely interact with co-ethnics and or work in labor market sectors that are dominated by co-ethnics (ethnic niches) are usually seen as not (yet) fully integrated into their new society. And when this also translates to the native-born children (so-called ‘second generation decline’), this is seen as problematic (Ganz, 1992). In this broader framework on integration and assimilation, Granovetter’s (1973) idea of strong and weak ties has entered the field of migration studies. Lang and Schneider, in this volume, rightly state that it is questionable whether the idea of strong ties – for co-ethnics – and weak ties – for ties with people without migration background – was originally intended by Granovetter to be used in this way. But what is clear, however, is that this idea fitted perfectly with broader theories on integration and assimilation. The importance for newly arrived migrants of strong co-ethnic ties in ethnic networks is generally considered one of the starting pieces of the puzzle laying out the process of assimilation in its first phase. The idea of weak ties, also in its symbolic emphasis on ‘weak’, perfectly suited the still scarce and superficial contacts with people of native descent in the early stages of the assimilation process. Since the concept of weak and strong ties fitted so well with the dominant theories about integration and assimilation (classical, neo and new assimilation), much of what was happening with migrants, and even their descendants, in the labor market was seen through, what many would call, an ethnic lens (Crul, 2016; Dahinden, 2016; Wimmer, 2013). Migrants gained a first foothold in the labor market through strong co-ethnic ties and were slowly moving up through their weak ties, making use of information and resources of people of native descent with whom they had only superficial contact. The idea of strong ties also resonated with the notion that their relations with co-ethnics were more meaningful and profound. There was also a dark side to strong ties. Under some conditions, because of the limited information and resources in the co-ethnic network, for some the strong ties could lead to an ethnic mobility trap.