Modern technologies and recently developed digital solutions make their way into all aspects of lives of individuals and businesses, and manufacturing industry is no exception. In the era of digital revolution of industry, manufacturing processes can benefit from digitalization technologies immensely. Digital twin (DT) is a technology concept that aims to create a digital mirror of a physical system with a constant data flow between two components. This idea can be used for monitoring and optimization of the present system as well as forecasting and estimating future states of it. There have been theoretical and practical studies conducted on DT in manufacturing area. This systematic literature review (SLR) aims to summarize the current state of literature and shine a light on open areas for future research. Using a rigorous SLR method, 247 relevant studies from 2015 to 2020 are examined to answer a set of research questions. The current state of DT in manufacturing literature is analyzed and explained with an emphasis on where the future studies may go in this area.