This book is devoted to the modeling and understandingof complex urban systems. This second volume of Understanding Complex Urban Systems focuses on the challenges of the modeling tools, concerning, e.g., thequality and quantity of data and the selection of an appropriate modelingapproach. It is meant to support urban decision-makers including municipalpoliticians, spatial planners, and citizen groups in choosing an appropriatemodeling approach for their particular modeling requirements. The contributorsto this volume are from different disciplines, but all share the same goal:optimizing the representation of complex urban systems. They present anddiscuss a variety of approaches for dealing with data-availability problems andfinding appropriate modeling approaches and not only in terms of computermodeling. The selection of articles featured in this volume reflecta broad variety of new and established modeling approaches such as: – An argument for using Big Data methods inconjunction with Agent-based Modeling;- The introduction of a participatory approachinvolving citizens, in order to utilize an Agent-based Modeling approach tosimulate urban-growth scenarios;- A presentation of semantic modeling to enable aflexible application of modeling methods and a flexible exchange of data;- An article about a nested-systems approach toanalyzing a city s interdependent subsystems (according to these subsystems different velocities of change);- An article about methods that use Luhmann s systemtheory to characterize cities as systems that are composed of flows;- An article that demonstrates how the Sen-Nussbaum Capabilities Approach can be used in urban systems to measure household well-beingshifts that occur in response to the resettlement of urban households;- A final article that illustrates how Adaptive Cyclesof Complex Adaptive Systems, as well as innovation, can be applied to gain abetter understanding of cities and to promote more resilient and moresustainable urban futures.