There is increasing evidence that a bilingual person should not be considered as two monolinguals in a single body, a view that has gradually been adopted in the diagnosis and treatment of bilingual aphasia. However, its investigation is complicated due to the large variety in possible language combinations, pre- and postmorbid language proficiencies, and age of second language acquisition. Furthermore, the tests and tasks used to assess linguistic capabilities differ in almost every study, hindering a direct comparison of their outcomes. Behavioral, electrophysiological, and neuroimaging data from healthy population show that the processing of second language domains (semantics, syntax, morphology) depends on factors such as age and method of acquisition, proficiency level and environment in which the second language was acquired. A number of single and multiple case reports that rely on behavioral testing of bilingual aphasics replicate these results. Additionally, they show that the patient's performance depends on the size and location of the lesion, as well as language typology and morphological characteristics. Furthermore, the impairment and recovery patterns and recovery generalization from treated to untreated language depend on the lexical and orthographic distances between the two languages. For healthy bilinguals, language processing is usually studied in comparison to monolinguals. We advocate that a good starting point for identifying patterns specific for bilingual aphasia is to compare patient studies of bilinguals and monolinguals. For further resources related to this article, please visit the WIREs website.