The systematic write-off of an asset over its useful life or some other predefined period. Depreciation and amortization are expenses which reduce income (but not cash), therefore effectively reducing potential tax liabilities. The Accounting Department in most organizations has the knowledge and documentation to expand or select amortization and depreciation methods and lives. Depreciation is a non-cash transaction. Of particular interest to Information Technology is the treatment of software purchase costs, which are typically amortized as non-tangible assets. (Costs to develop software, unless it is for resale must generally be expensed.)