Mental capacity is the ability to retain, process, and weigh up information to provide a completely objective decision independent of any cognitive impairment present. Awareness of an individual’s mental capacity is important for all healthcare professionals. Mental capacity and capacity assessments are guided by the legal framework; the Mental Capacity Act 2005. Mental capacity assessments enable practitioners to determine if a patient is able to make reasoned decisions independently, or whether the patient requires assistance in their best interests and are decision and time dependent. Therefore, capacity can fluctuate over time and if someone is deemed to have no capacity on one occasion this does not mean that they should be assumed to consistently lack capacity. The act delivers five key principles to follow in order to determine whether an individual has or lacks mental capacity.