What Can generalized social trust (trust in unknown others)-the social cement that connects individuals across different segments of society-be maintained in the face of increased immigration and the ethnic diversity that follows from it? Synthesizing and expanding on my previous work, the book project addresses this fundamental and highly pertinent question. It articulates the theoretical mechanisms by which immigration may erode social trust, and put each of these to a stringent empirical test using the best-suited data and research designs currently available. The resulting monograph will generate key insights into the consequences of one of the most significant developments of our time as well as provide a richer theoretical understanding of the processes by which trust are formed. Why The project speaks directly to one of the most hotly debated issues of our time: can social cohesion-here indicated by social trust-be maintained in the face of increased immigration and the ethnic diversity that follows from it? Despite the obvious relevance, a systematic theoretical account to understand the relationship between ethnic diversity and trust has not yet been developed, and the corresponding empirical evidence has been scattered and not well informed theoretically. Against this backdrop, the monograph seeks to provide a stringent theoretical account for why immigration may erode social trust, and put this to a rigorous empirical test. How Conceptually, I will articulate how I understand generalized social trust-as a belief about the trustworthiness of unknown others-and thereby seek to clarify why most previous conceptualizations have misunderstood or simplified this concept, and thereby, in turn, obscured the purported relationship with ethnic diversity. In the empirical analyses, I draw on a range of Danish and international data on immigrants and natives to shed light on the mechanisms by which ethnic diversity may erode trust. SSR The project shows Scientific Social Responsibility by addressing what is not only one of the most pertinent contemporary questions, but also an issue that is likely to increase in importance over time given the ongoing demographic shifts. Furthermore, from the conclusions of the study, we will learn about not only the consequences of immigration for social trust, but also get some directions as to how harmonic and successful co-habitations between social groups can be obtained. Applied research can subsequently derive more specific policy interventions based on these insights.