This area of IFRS accounting was substantially revised in 2003 to move IFRS into line with the changes in US GAAP on goodwill and business combinations. The basic approach of IAS 38 Intangible Assets is that only purchased intangibles are recognized, and their subsequent measurement may be on a cost basis or a valuation basis. In line with the Conceptual Framework, an intangible is recognized only if the entity has control over it, and if future economic benefits are expected to flow from it, and it can be measured reliably.
In addition to the standard asset definition, IAS 38 adds that an intangible must be separable or must arise from contractual or legal rights. Separability is the ability to sell or transfer the asset, either individually or in conjunction with another related asset or liability. If the asset is carried on a cost basis, it is subject to amortization and impairment. If it has a finite useful life, the cost is amortized over this and it is normally assumed that there is no residual value. If the asset is considered to have an indefinite useful life, then it is not amortized but it must be checked annually for impairment (as well as at any time there is an indication of impairment).
As regards specific kinds of asset, goodwill arising on consolidation is addressed in IFRS 3 Business Combinations and does not have to meet the IAS 38 criteria for an intangible asset (e.g. it is not separable, and some people do not think it is an asset, although ...