The Mental Capacity Act (MCA) has been in force in England and Wales for over a decade. Although often considered in relation to health and social care, the MCA also governs the inclusion of people with cognitive impairment in research. This includes procedures for establishing whether prospective participants are able to consent to participation. Despite its importance in research, there is little literature detailing accounts of researcher’s experiences of working with the MCA’s decision-making capacity procedures when conducting research. To address this deficit, we present our experiences when conducting three separate studies involving people with dementia and therefore falling within the MCA’s research provisions. Study A (data collected between September 2016 and April 2017) discusses the subjectivity of capacity assessment; Study B (data collected between July and November 2017) details the negotiation of different opinions on capacity; and Study C (data collected between January and October 2013) considers tensions between legality and the principle of non-maleficence. Each of these experiences indicates a problematic degree of uncertainty within the MCA’s decision-making capacity provisions. We suggest two solutions. First, more detailed guidance is required, responding to uncertainties emerging in practice. Second, researchers should be encouraged to publish their experiences of working with the MCA. In outlining our own experiences, we hope to initiate such a body of work.