The research comprised in this graduation report aims to establish a framework and design approach to the re-purposing of the Hagia Irene church in Istanbul. It seeks to answer the following research question: “How can we preserve the specific characteristics of the Byzantine church Hagia Irene in Istanbul when introducing a new function?” This question is approached by first analyzing the church’s historical and present-day characteristics, as well as those of its surroundings. Historical characteristics include the basilica plan, the dome, the contrast between the exterior brick and interior mosaics, and the connection with the Hagia Sophia. During the Ottoman empire, the connection with the Hagia Sophia was severed by the construction of the courtyard wall of the Topkapi Palace. As well, the Byzantine urban fabric was covered with 6-8m of sand, and a new Ottoman layer built over it. The ruins of these historical layers are a defining characteristic of the Hagia Irene, and have been preserved in what is now an archaeological park around the church. Today, some of the Hagia Irene’s characteristics have been lost, in part because the mosaics have been worn away, and because most of the doors and some of the windows have been filled in. The second section of the report outlines different approaches to re-purposing historical buildings, with a focus on Istanbul’s Orthodox spiritual leaders and architects. The spiritual leaders are against the re-purposing of churches, because a place built and consecrated for worship should not be used for anything else. However, they allow combining the church’s original function with other appropriate uses such as a concert hall or museum. They also suggest to focus on the church’s surroundings for the addition of new functions. Istanbul’s architects also stress the importance of maintaining a continuity with the history of the church, especially with its original architectural and urban characteristics. In this way, the integrity of the space can be preserved. The third section explores two case studies of interventions that re-purpose historical buildings while preserving their original characteristics. The first is the Szathmáry Palace in Hungary, which re-purposes a bishop’s summer residence from the 16th century into a theatre by adding an enclosed staircase and sitting elements. The new elements contrast with the ruins while, at the same time, emphasizing the original structure. A similar approach is adopted for the re-purposing of Astley Castle in the United Kingdom. The new layer that is added to the medieval castle both strengthens the ruins structurally, and frames them visually. The report concludes that, in order to preserve Hagia Irene’s specific characteristics when introducing a new function, new additions should maintain the integrity of the architectural space, restoring and bringing attention to its character-defining structural and decorative elements, at the same time making reference to the building’s history. While multifunctionality should be provided for, the church’s original function should be respected. Based on the research conclusions, design principles are formulated. They address the church’s interior, the adjacent ruins, and the overall surroundings, and express the design’s aim to give importance to the experience of the Hagia Irene’s history by framing its “layers of time”.