折旧（英语：Depreciation）在会计学是指在一个期间使用的部分使其提列成资产的减少以表示使用的纪录。例如房屋及建筑就是其中一个须提列折旧的物品。但是土地不需提列折旧，因为土地的总供给数量通常是固定不变的。配比原则的一个例子就是固定资产的折旧，固定资产可以贡献企业营运的经济效益在一会计期间以上，即使如此，其效益也会随着时间的经过而为企业营运所耗用，也就是为了创造企业的营业收入提供其服务效益，所以依据收入费用配合原则，固定资产的成本必须在其提供服务的会计期间逐期转列为费用，作为相关营业收入的减项，以计算营业损益，这个有系统的将固定资产成本转成费用的方式，称为「折旧」。

In accountancy, depreciation refers to two aspects of the same concept:

A method of reallocating the cost of a tangible asset over its useful life span of it being in motion. Businesses depreciate long-term assets for both tax and accounting purposes. The former affects the balance sheet of a business or entity, and the latter affects the net income that they report. Generally the cost is allocated, as depreciation expense, among the periods in which the asset is expected to be used. This expense is recognized by businesses for financial reporting and tax purposes. Methods of computing depreciation, and the periods over which assets are depreciated, may vary between asset types within the same business and may vary for tax purposes. These may be specified by law or accounting standards, which may vary by country. There are several standard methods of computing depreciation expense, including fixed percentage, straight line, and declining balance methods. Depreciation expense generally begins when the asset is placed in service. For example, a depreciation expense of 100 per year for five years may be recognized for an asset costing 500.