Despite a plethora of good advice, it can be hard to sustain effective communicative behaviours when someone is living with a dementia. This book asks why that is. Part 1 explores how various dementia-causing diseases affect the linguistic, pragmatic (reasoning), and memory systems; how social perceptions and practices exacerbate the underlying biological problems; how people living with a dementia describe their experiences; and how dementia care currently addresses the challenges of communication. Part 2 asks why people communicate and what shapes how they communicate. The Communicative Impact model of communication is introduced and theoretically justified. It is argued that all communication is driven by people’s desire to make beneficial changes to their experiential world by getting the hearer to do, say, think, or feel something. Part 3 applies the model from part 2 to the range of considerations explored in part 1, helping readers see how and why communication is undermined and reshaped by the various biological, social, and emotional factors underlying the dementia experience. The model is used to shed light on how people living with a dementia are perceived and, as a result, treated, with particular attention to the acceptability of (well-intentioned) deception. The final chapter asks what needs to change if communication and well-being are to be optimized for people living with a dementia. In pursuit of truly person- and relationship-centred care, proposals for advanced skills in communication with a person living with a dementia are presented and explained, helping anchor the ubiquitous dos and don’ts in a deeper understanding of why interaction is difficult.