The increasing prevalence of dementia amongst older adults, particularly coupled with a ‘greying’ population, is a major issue that our society faces over the next few decades. Dementia, now known as major neurocognitive disorder, encompasses a range of conditions such as Alzheimer’s disease, vascular dementia, and mixed type dementia and is more prevalent amongst adults with intellectual and developmental disabilities (IDD). Behavioural gerontology, the application of behaviour analysis to the problems of older adults, remains a smaller area of research for behaviour analysts than other areas such as autism and education. Despite this, there have been significant contributions to the quality of life of adults with dementia through the application of behaviour-analytic principles. In order to develop interventions to improve quality of life through changing the environment, behaviour analysts must first conduct assessments of the controlling variables of target behaviours. The purpose of this thesis was twofold. Firstly, we aimed to contribute to the behaviour-analytic literature regarding the use of assessments with adults with dementia in care home settings, the results of which may inform interventions to improve quality of life. The study presented in Chapter 2 evaluated the use of experimental and descriptive analyses of problem behaviour with two adults with dementia to determine if they provided results that would indicate the same function of behaviour. Chapter 3 describes an assessment comparing simultaneous and sequential presentations of choice to determine the preference of adults with dementia for different social contingencies. In Chapter 4, we utilised preference assessments to determine the preferences of adults with dementia with and without IDD for edible and leisure stimuli. Finally, the second purpose of this thesis is addressed in Chapter 5 in which we identified and evaluated the extent of behaviour analytic research specifically with an understudied population; adults with intellectual and developmental disabilities and dementia.