The accuracy of neuropsychological assessment is critical in the diagnosis of cognitive impairments in older adults. However, existing neuropsychological tests may not be suitable for minority populations. This thesis aimed to address this issue by recruiting cognitively-healthy South Asian older adults and assessing cognitive function in this group. Results showed that typically used assessments, despite being translated, were not suitable for this cohort. Furthermore, skills required for test completion such as mathematics and writing/hand dexterity (which are related to education levels) influenced test scores. Therefore, new assessments of general cognitive function and associative memory were developed to improve the accuracy of neuropsychological test scores. The new tests were not affected by education and they achieved high internal and test re-test reliability. Time of day (TOD) that testing takes place is also known to affect cognition. Interestingly, no TOD effects were observed in this cohort. It was hypothesised that engagement in the daily five Islamic prayers may have contributed to this lack of a TOD effect. However, the results did not confirm this. The thesis then looked at overall prayer engagement and cognition. Results showed that engagement in the daily five prayers and Quran recitation significantly increased scores on assessments of processing speed. This thesis demonstrates that accurately assessing cognition in South Asian older adults is challenging and that the cognitive tests used must be suitable for this cohort. Interesting findings emerged for prayer engagement which may have wider implications for the field of cognitive reserve.