Planning, design and development of sustainable buildings and communities requires a holistic approach and an assessment of local conditions, climatic and environmental effects, passive design strategies, energy consumption, renewable energy sources, material use and cost. Strategic planning from the earliest stages of the design is necessary since site-specific conditions and considerations for the local environment need to be addressed. This article presents relationships between building simulation tools and sustainable design in practice as well as impact of computational tools during the decision-making process. Different types of analyses are discussed that need to be performed in order to understand building site and context, environmental conditions, availability of daylight, innovative building technologies and potentials for utilization of renewable energy sources. Initially, a brief overview of past research on the utilization of computational tools for the decision-making process in sustainable design is given. The second part of the article discusses sustainable design approaches and lastly, three case studies from an architectural practice are presented that illustrate analysis procedures that support the decision-making process. The first example illustrates environmental analysis and design strategies for a science and technology facility. The second case study portrays an examination of building envelope properties and daylight optimization for a healthcare facility. Lastly, the investigation of a building integrated photovoltaic system for a sports and recreation facility is discussed, where energy output and life-cycle costs are examined.