Roadside units (RSUs) are roadside infrastructure that can improve the communication between autonomous vehicles and infrastructure in an intelligent transportation system (ITS) at the cost of being expensive to implement. The problem of maximizing the benefit an RSU network provides while minimizing cost is called the RSU placement problem, which has been widely researched due to its potential benefit. Despite this, there is not a comprehensive survey of the topic to the best of our knowledge. The goal of this paper is to bridge this gap by providing a single source for future researchers to use to better understand the state of this topic. The paper focuses on three main topics; formulating the problem into an optimization problem, determining the objectives used to measure the RSU network’s performance, and the algorithms that are applied to solve the problem. A description of the different methods is provided along with examples found in the literature. The paper concludes with a discussion of challenges faced by authors and promising future research directions. We hope this survey will serve as a guide for readers on the approaches that can be used for the RSU placement problem and help facilitate new research in the field.