Five Whys is a simple tool used to identify the root cause of a particular problem by repeatedly asking the question “Why”, drilling down through the layers of symptoms and determining the cause-and-effect relationships. It is important to recognize that there is nothing special about the number five. In fact, the root cause of the problem may be identified after asking the question “Why” only two or three times. In other cases, it may take more than five iterations to uncover the root cause. The Five Whys is most effective when the answers come from people who are closest to the problem being investigated. The root cause needs to be validated by additional data collection, analysis and testing. The Five Whys is generally used in combination with other tools and techniques such as the Cause and Effect Diagram, Pareto chart and Brainstorming. The Five Whys provides several benefits including meaningful employee participation in improvement initiatives, high degree of flexibility and adaptability in dealing with different situations, rapid identification of the root causes, and reduced likelihood of implementing superficial solutions that are not effective in the long run. This tool is also very easy to use and understand. However, most complex or safety-critical problems require the use of more advanced tools and techniques in order to perform an in-depth analysis of the latent conditions, fully understand the interconnectedness between the various elements of the work system, and ultimately identify sustainable solutions.