Congestion and congestion management are the extended meaning of transmission reliability and control's concept in electricity market environment. The paper annotates congestion management's essentials and their classification， discusses congestion pricing and congestion cost allocation problems from various viewpoints， such as description of the problem， mathematics models， objective functions， constrains， control variables and control strategies. The relationship between congestion and security， as well as that between congestion management and stability control， are pointed out. Recent status and further developments of congestion management studies are reviewed.