From ancient times till today dome structures have served as a distinguishing characteristic of the Iranian townscape. As such, dome structures are an inseparable element of Iranian architecture. The oldest still preserved structures were built in the 3rd century AD, during the reign of the Sasanian dynasty. Over time and with growing sophistication of the applied engineering techniques, the architects were able to refine these structures and establish a system consisting of few basic constructive elements that can be creatively deployed to effect a large variety of construction options. From an engineering perspective a domed structure consists of three main elements: The dome base or body, the connecting element and finally the dome itself. Traditionally, most Iranian dome structures are built on a body with a square shaped ground plan. The connecting element serves to provide a transition from the polygonal (in our case mostly square shaped) dome base to the spherical dome. The squinch has an artistic or decorative role, but also a constructive or engineering role in the building. The engineering role consists of being a platform that can sustain the weight of the dome. From an artistic perspective, it serves to fill the empty space that is inevitably created in a transition zone when a spherical dome is set on top of a polygonal base. It is impossible to distinguish between the engineering and artistic roles in the early dome structures from the third century AD. A major innovation that happened in the 10th century AD was the introduction of the load-bearing arch that made it possible to separate the artistic from the engineering aspect of the squinch. This led to an explosive spread of creative ideas for the decorative design of a dome structure-s interior and exterior space. This thesis begins with an overview of the development of dome structures in the Iranian architecture. Subsequently it provides a detailed analysis of the differences in construction of the dome and the connecting elements, respectively. This includes the main historical milestones of their development. In particular, we shall discuss the construction techniques in the context of their time, as well as consider the influence of geographical circumstances and available building material. The domes and squinches will be classified based photographical evidence and analysis of construction plans and documented with three-dimensional illustrations.