Despite the improvement in utilization of project management tools and techniques over the years, there are still many projects failed to meet their objectives. Early warning signs becomes one of the concepts used to detect the potential cause of failure in a project. Early warning is defined by signals, which can be seen variously as an expression, indication, a proof, or a sign of existence of some future negative issues. In recent years, several researches regarding early warning signs have been proposed by many authors, varying from project assessment stage in detecting the signs, methodology in conduction early warning sign research and the type of the projects tested. This article presents a review of related work on early warning signs of project failure to give conceptual insights on what early warning is. © The Authors, published by EDP Sciences, 2018.