Caffeine is the most frequently consumed stimulant worldwide and has been championed as an attentional enhancer in clinical trials for over a hundred years. There is broad agreement that caffeine induces an attention enhancing effect. However, a minority disagree and propose the caffeine withdrawal reverse hypothesis. This posits that, due to inadequate caffeine withdrawal procedures in study design, the beneficial properties displayed by caffeine on attention result from reversal of caffeine withdrawal. In caffeine studies with an appropriate withdrawal period prior to intervention, no clear beneficial effect on attention has been demonstrated. This thesis critically appraised the literature and using a novel experimental paradigm, explored the utility of caffeine as an attentional enhancer in participant groups consisting of healthy elderly, dementia with Lewy bodies (DLB), Parkinson's disease (PD) and multiple sclerosis (MS) sufferers. I conducted a blinded, randomised controlled, cross over design trial to explore whether caffeinate improved performance on experimental and real-world tasks of attention. I systematically assessed three broad areas of attention: alerting, orienting and executive networks with neuropsychometry tasks aligned to each domain. These experiments are unique within the literature as they combine a complete caffeine withdrawal period prior to intervention, a systematic approach to assessing for attentional enhancement and patient cohorts not previously investigated in relation to the attentional effect of acute caffeine ingestion. I conclude caffeine is not an effective attention enhancer, at least not in populations of healthy older people or people with PD or DLB. The possibility remains that caffeine may enhance attention in people with MS and perhaps in other situations such as sleep deprivation.