With the tight integration of computation and communication into the power system, the Smart Grid has become a large Cyber Physical System, with complex cyber and physical, inter- and intra-domain, interactions and interdependencies. A multi-domain modeling approach is, thus, required to be applied for the modeling of such systems, as it is no longer possible to model the participating domains independently. Monolithic approaches are not practical due to their lack of details and adaptability. An attractive alternative is co-simulation, but such tools/methods are not widely available due to scarcity of native coupling interfaces to analyze two-way communication, enhanced automation, monitoring and control, self-healing capabilities, and increased hosting of renewable energy resources. The aim of this dissertation is to investigate and develop a flexible, extendable and co-simulation based tool-set for analyzing emerging behaviors and resulting effects of power systems with tight integration of communications and controls. Such a tool-set is developed, capable of providing fine-grained and detailed dynamical simulation of power, communication and control systems. By utilizing well-known, domain specific and specialized tools, it enables collaborations and makes it possible to reuse existing models and know-how, improving the reliability and reducing the efforts, considerably. Due to a strong focus on development of generic coupling interfaces, the tool-set enables easy integration of many other tools, enabling rapid adaption and making the tool-set highly applicable in many areas of Smart Grid design and analysis. The usability and applicability of the proposed tool-set has been demonstrated with three diverse case studies, where varying communication infrastructure models, technologies and scenarios are investigated. The tool-set show effects of different communication infrastructure parameters on the performance of the Smart Grid, using the key performance indicators from leading European Smart Grid research projects. Collected results identify a non-linear relationship between Smart Grid and communication infrastructure performance. Parts of the tool-set have been used and validated in two European research projects.