Polyethylene is one of the most widely used polymers in industry as fiber, film and bottle because it has many advantageous properties such as easy of processing, high chemical resistance, flexibility, low density and adequate mechanical properties and low cost.There are various commercial technologies available to produce all the range of polyethylene grades including high pressure PE processes, low pressure PE processes and bimodal or multi-modal PE processes.In principle, PE plants are so-called swing units which are able to produce both HDPE, MDPE and LLDPE, even if cost-wise it is better to avoid frequent switches between the PE grades with different densities.The gas phase polyethylene production process is the most recently developed low pressure PE process and boasts many distinct advantages when compared with the commercial slurry and solution processes.There are three major kinds of gas phase polyethylene production processes: single fluid-bed reactor configuration, dual cascade reactor configuration and hybrid process.Some of the most important licensors which produce swing units polyethylene are Unipol (Licensed by Univation), Innovene G (Licensed by Ineos), Spherilene (Licensed by LyondellBasell) and Borstar (Licensed by Borealis).These famous licensors and their proprietary processes will be reviewed in detail.This paper also reviews the historical development of swing units gas phase polymerization technology as well as the development of catalyst from Ziegler-Natta catalyst to metallocene-based catalyst.A critical review of the challenges and opportunities from an industry view-point is presented.In the end, some suggestions on domestic LLDPE/HDPE Polyethylene development were also given.