Background: People with aphasia (PWA) typically exhibit deficits in spoken discourse. Discourse analysis is the gold standard approach to assess language deficits beyond sentence level. However, the available discourse assessment tools are biased towards English and European languages and Western culture. Additionally, there is a lack of consensus on which discourse measures to use and limited evidence of the psychometric properties of published discourse measurements. Aims: (1) To develop a standardized, norm-referenced, culturally and linguistically appropriate Arabic Discourse Assessment Tool (ADAT); and (2) to examine the psychometric properties of content and construct validity and interrater reliability of different discourse measures elicited using three discourse genres (descriptive, narrative and procedural) in neurotypical control adults and matched PWA. Methods & Procedures: Discourse samples were collected using three novel discourse stimuli that are sensitive to the Arabic language and culture from 70 neurotypical control adults and a matched group of 50 PWA. Transcription agreement was assessed. A standard approach was used to evaluate construct validity and interrater reliability for 16 discourse measures that assess fluency, language productivity, information content, lexical--semantics, lexical diversity, grammatical category, grammatical structure and syntactic complexity. Strong measures were identified based on their psychometric properties, and normative data were established on these measures. Discourse performance of PWA was then examined using the newly developed tool (ADAT). Outcomes & Results: Transcription agreement was extremely high for all discourse stimuli in both groups. Eight discourse measures were proven to have consistently very high construct validity and consistently very good to excellent reliability across the three stimuli in both neurotypical control and aphasia groups: lexical information units, content information units, words per minute, discourse duration, number of different words, number of complete sentences and proportion of open and closed class words. Norms were established on these measures, and cut-off scores of impairments were determined. Other measures showed low construct validity and variable or poor reliability across the two groups. Conclusions & Implications: The newly developed, standardized, and norm-referenced tool (ADAT) consist of three discourse stimuli and eight high-quality discourse measures that assess multiple aspects of spoken discourse and were able to differentiate PWA from neurotypical adults consistently. ADAT also includes normative data and cut-off impairment scores. The tool has great potential to enhance clinical practice and research with Arabic speakers. Evidence was provided that not all discourse measures are of high quality, as some are vulnerable to differences between raters, discourse stimuli and groups. Clinicians and researchers can use ADAT for accurate aphasia assessments, better management plans and to monitor therapy effectiveness. ADAT can be further validated in other clinical populations with language impairments.