## 1 Introduction  
The built environment consists of human-made buildings and infrastructures such as commercial and residential buildings, bridges, roads, tunnels, storage tanks, and pipelines. These structures must be routinely inspected and monitored both during and after construction. The structure is monitored and assessed through regular inspections performed by different stakeholders including owners, project managers, architects, engineers, contractors, sub-contractors, end users, and facility managers [1]. Irrespective of who is performing the inspection, manual inspection is a time-consuming process and adds to the project cost [2]. Manual inspection is also characterized by a high degree of variability in the quality of assessment and subjectivity [3, 4]. Some inspection tasks are difficult for humans to perform due to inaccessibility, e.g., confined spaces such as inside air-conditioning ducts [5, 6], water-filled pipelines and tunnels [7], offshore structures [8], and small spaces in walls [9]. Some situations might be hazardous for humans, such as inspection at heights [10], structures subjected to natural disasters [11], or a bridge deck [12]. Different inspection and monitoring activities differ in their requirements and face different challenges. Therefore, not all types of inspection can be performed by the same robot. This review paper identifies robot types and various application subdomains within the domain of inspection and monitoring of the built environment and discusses their challenges. Robots have been used in building and infrastructure projects in many ways--e.g., for concrete production, automated brickwork, steel welding, concrete distribution, steel reinforcement positioning, concrete finishing, tile placement, fireproof coating, painting, earthmoving, material handling, and road maintenance [13]. Robots with many different locomotion types and sensors have been used for the inspection of the built environment [3]. Some examples are unmanned aerial vehicles (UAV), unmanned ground vehicles (UGV), marine vehicles, wall-climbing robots, and cable-crawling robots, among others. Robotic inspection provides a safer alternative to manual inspection [14, 15]. Automated robotic inspection improves the frequency of inspections and reduces subjectivity in detecting errors [16, 17, 18]. As described in this review, challenges associated with developing and implementing robots for inspection and monitoring of the built environment are substantial. One of the biggest challenges is that buildings and infrastructure differ widely in design and intended use. Programming and designing a robot to operate in a wide range of input environments is a significantly difficult task [3]. Furthermore, various inspection subtasks need completely different robot functionalities, such as defect detection [19], progress estimation [20], and resource tracking [21], among many others. During this review, it was identified that previous research can be categorized into distinct research areas based on what challenges it addressed. All these research areas are identified, and the findings are presented in this paper. [PERSON] and [PERSON] [22] presented a comprehensive review of the use of drones for building inspection. However, the current review includes all types of robots, including but not limited to drones. [PERSON] and [PERSON] [3] reviewed the literature on the robotic inspection of infrastructure. They studied different types of robots based on their mobility. They also studied different methods developed by past researchers for improving the autonomy and damage perceptions of these robots. However, there have been numerous advances In the field of robotics, and in their supporting technologies, such as computer vision and deep learning recently. In fact, a bibliometric analysis of the papers reviewed in this study revealed that more than 60% of the papers analyzed were published after 2017, when [3] published their review. The results of the bibliometric analysis are presented in Section 3.