Chunyun (traditional Chinese: 春運; simplified Chinese: 春运; pinyin: Chūnyùn), also referred to as the Spring Festival travel season or the Chunyun period, is a period of travel in China with extremely high traffic load around the time of the Chinese New Year. The period usually begins 15 days before the Lunar New Year's Day and lasts for around 40 days. The number of passenger journeys during the Chunyun period has exceeded the population of China, hitting over 2 billion in 2008. It has been called the largest annual human migration in the world.Rail transport experiences the biggest challenge during the period, and myriad social problems have emerged.

Three main factors are responsible for the heightened traffic load during the Chunyun period.

First, it is a long-held tradition for most Chinese people to reunite with their families during Chinese New Year. People return home from work or study to have Reunion dinner with their families on New Year's Eve. Since the Chinese economic reforms of the late 1970s, new economic opportunities have emerged, often at a considerable distance from people's hometowns. Places such as the Special Economic Zones and the wealthy coastal regions offer employment and often, a more sought-after lifestyle. Consequently, there has been a massive migration from rural to urban areas over the course of the last few decades, reminiscent of other industrial revolutions around the world. The number of these migrant workers was estimated at 50 million at 1990 and unofficially estimated at 150 million to 200 million in 2000. During the Chunyun period, many of these laborers return to their home towns.