Language breakdown after stroke has been extensively studied in the aphasiology literature. However, strokes are diffuse lesions and can result in cognitive impairments beyond language, in domains such as attention, executive functions, memory and visuospatial deficits. Recent research has focused on cognitive abilities in aphasia and how they relate to linguistic impairment. Moreover, the accurate assessment of cognition is important for a variety of reasons, including to determine the extent of cognitive deficits beyond language and for rehabilitation planning. This thesis aimed to examine the relationship between semantic processing and cognition in aphasia, as well as to discuss current cognitive assessment practices in aphasia. A variety of methods were used to investigate these issues: a critical and a systematic review, an experimental study and a survey.Following an introductory overview (Chapter 1), two chapters focus on the relationship between semantic processing and executive control in aphasia. Chapter 2 examines the role of cognitive abilities in semantic processing tasks and presents a critical review of the Controlled Semantic Cognition account. Chapter 3 tests the prediction from the Controlled Semantic Cognition account that associative errors in naming tasks are a consequence of semantic control deficits and which other factors may influence the occurrence of associative errors.The next two chapters focus on practices regarding the assessment of cognition in aphasia. Chapter 4 presents a systematic appraisal of the tools used to assess cognition in studies with aphasia published from 2010 to 2020. Chapter 5 explores aphasia clinicians’ and researchers’ views on the current practices of assessment of cognition in aphasia. Finally, in Chapter 6, the main results are discussed considering their contribution to our current understanding of the relationship between cognition and language in aphasia.Overall, this thesis presents results that underscore the importance of accurately assessing cognition in aphasia and provides an overview of assessment practices in the research and clinical context. In addition, it contributes to the knowledge of semantic processing in aphasia and how it relates to cognitive processing.