Network security analysis and optimization forms the core of the advanced application software in modern power system energy management systems. Recent progress in network security analysis and optimization is reviewed in this paper. Topics include state estimation, observability analysis, bad data processing, topology error detection, parameter error estimation, external network modelling, contingency selection, optimal power flow, corrective rescheduling and constrained economic dispatch. Issues concerning modelling, assumptions and limitations, solution methods, computational efficiency, solution accuracy and applications are addressed. Future trends in research are also discussed.