Digitization is seen as a central force in order to transform the public sector to become transparent, participative, collaborative as well as efficient. In order to realize the digitalization, a public organization need to have an IT architecture that can support such a transformation. Therefore, decision makers in a public organization need to make informed decisions when governing, designing and implementing an IT architecture. This require that they have an understanding of the alternatives available to them in terms of possible IT systems and their roles in the organization’s overall IT architecture. However, there is a lack of concrete descriptions providing such an understanding. In this chapter we present a number of types of IT system that public organizations could or need to have as part of their IT architectures; the problems these types of IT system address; what alternative IT systems and technology solutions are available for each type of IT system; and guidelines on what alternative solutions to select given the situation or condition at hand in a public organization. The chapter also includes a description of the relationships between the various types of IT systems and clarifies their roles by means of a business and IT architecture. The business and IT architecture, the different alternatives and guidelines are based on experiences from a number of research projects within the public sector. Real-life examples from the projects illustrate the alternatives proposed.