Objective: Urban annexation is an emerging phenomenon in developing countries, including Iran, which occurs as a result of the horizontal expansion of metropolises and the confrontation of city and suburban systems; in such a way that peri-urban settlements gradually acquire urban characteristics and are annexed to them. In this process, various types of settlements around metropolises have emerged, which have different contextual characteristics, and these characteristics also have a significant impact on the extent of annexation of peri-urban settlements to metropolises; in such a way that the first step in analyzing the annexation of settlements around metropolises is to identify the types of peri-urban areas through their typology as a systematic method for in-depth analysis of the types formed and the general lack of contact with peri-urban settlements. Therefore, the aim of the present study is to explain the annexation of various types of peri-urban settlements to metropolises - specifically Mashhad - to find out why and how it occurs. Research Method: The research method in the typology stage of settlements around the Mashhad metropolis is quantitative and through cluster analysis (K-Means) and in the second step, qualitative with a descriptive-analytical approach and based on documentary, library studies and field surveys. Findings: Settlements around the Mashhad metropolis were classified into three types based on three factors: construction-oriented, community-oriented and nature-oriented into three types: urban (with dominant urban characteristics), urban-rural (with simultaneous urban and rural characteristics) and rural (with dominant rural characteristics). The results of the present study also indicate that the degree of integration of peri-urban settlements into metropolises varies based on the location and the manner of mutual relationship between population and building density and the area of the peri-urban settlement relative to the city, the type of relationship between the city and the periphery, and the manner of development of the peri-urban settlement. Conclusion: Based on what was explained in this study, it can be concluded that the incorporation of various types of peri-urban settlements into metropolises can be explained and analyzed based on the approach to dealing with them based on two main factors: the location of the peri-urban settlement relative to the neighboring city and the type of transformation of the peri-urban settlements. This research reveals more than ever the necessity of preparing and formulating specific plans for peri-urban settlements based on a new approach and based on combined urban and rural characteristics. Of the three types extracted in the present study, only the first type fits into the framework of urban plans due to its location in the current city, and the second and third types require special urban and regional planning at the micro and macro levels.