What is Six Sigma and how is its implementation? The studies on Six Sigma have been developing in recent decades, but the discussions on the topic are fragmented and thus challenging to understand comprehensively. This study aims at answering what Six Sigma is and how it is implemented in both manufacturing and non-manufacturing industries. To do this, we conduct a literature review on journal articles published from 2000 to 2017. Six Sigma has beena commonly used method among companies around the world for increasing product quality and operating profit. It is not only used in the manufacturing industry but also in non-manufacturing industries. The finding shows that Six Sigma is a method used to minimize the number of defect products and increase customer satisfaction as well as profit. In its development, Six Sigma is also used as a statistical tool, a managerial philosophy, and a business culture. Although it can be seen from various perspectives, the core of Six Sigma lies in its method, which is based on the scientific approach for developing efficiency and increasing operating profit. In general, the studies on Six Sigma have begun increasing since 2004. In the manufacturing sector, studies on Six Sigma are prevalent in automotive, electronic, and SME sectors and in the non-manufacturing sector, studies are common in the health and educational sectors