走私，是指携带未经落地海关检查及报税的货物过境之非法行为。另外走私人口参见偷渡与贩卖人口。走私分为两种途径：

走私原因很多，主要为了逃避关税，或者进口违禁产品。

过去中国大陆对多项产品征收关税，使不少洋酒公司都透过走私的方式运送洋酒进中国大陆；而澳洲亦有不少人为免利润微薄的电子产品因为销售税而使订价过高，而透过走私途径入口产品。

而对于非法产品，主要都是毒品、枪械或违禁药品的入口。此外，在中国大陆，亦有不少人从事赃物走私。不少在香港被盗的右軚车及投影机，都是透过内河船走私进中国大陆转售。另一方面，对于监管极严的地区，走私亦是另一种方法去为高需求商品提供运输的途径。冰鲜肉类曾经是香港常见的走私货品，而在新加坡，由于不准公开发售烟草及口香糖，这些商品都要依靠走私。

Smuggling is the illegal transportation of objects, substances, information or people, such as out of a house or buildings, into a prison, or across an international border, in violation of applicable laws or other regulations.

There are various motivations to smuggle. These include the participation in illegal trade, such as in the drug trade, illegal weapons trade, illegal immigration or illegal emigration, tax evasion, providing contraband to a prison inmate, or the theft of the items being smuggled. Examples of non-financial motivations include bringing banned items past a security checkpoint (such as airline security) or the removal of classified documents from a government or corporate office.