Well completions are an integral part of providing safe, reliable and continuous access to underground resources such as oil, gas and geothermal resources. Completions are typically considered to be the final step of drilling engineering which includes processes such as setting casing, cementing, and perforating to reach the target formation. Completions provide the conduit from the resource to the surface. Although completions encompass a wide range of disciplines, several key factors ultimately determine the quality of the completion. One of those is cementing and centralizing casing within the wellbore. This white paper examines the current state of the art for centralizers in the context of well completions. The paper will include an introductory primer on well completions to provide the framework for the centralizer discussions. The types of centralizers currently available and how they are used will be discussed in addition to alternative centralizer techniques.