Aphasia is an acquired language disorder caused by focal brain damage, which affect all modalities of language. Therefore, segregation of aphasia from speech disorders or modality specific problems such as dysarthria, apraxia of speech or agnosia is the first step of differential diagnosis. Even though cognitive dysfunctions affect language performance, cognitive communication disorder is also a different concept from aphasia which in confined to pure language disorders. The purpose of this study is to introduce various models and methods of evaluation on aphasia and to review of recent issues of aphasia research.