Heterogeneous chromium catalysts are widely used for the ethylene polymerization.The discovery of homogeneous model systems has substantially improved our understanding of the underlying organometallic chemistry and is fueling the current round of innovation hailed as "metallocene technology". Despite their commercial importance

chromium catalysts have inspired less modeling activity

owing possibly to the paramagnetism of relevant organometallic complexes.The potential for paramagnetic organochromium synthesis has brightened in recent years

in part due to technological advancements.The use of single-crystal X-ray diffraction method has dramatically decreased the measure difficulty of chromium complexes

to the point where X-ray structural determination has become almost mandatory for confirming the identity of all new paramagnetic products.The growing demand for high performance polyolefin products in recent years has inspired extensive industrial and academic interest to develop high performance novel homogeneous chromium catalysts.This paper summarizes the latest progresses in chromium based homogeneous catalysts and their application in olefin polymerization.