It is a professional requirement of nursing regulators such as the Nursing and Midwifery Council and the Nursing and Midwifery Board of Ireland that all nursing interventions should be based upon, and underpinned by, an accurate and structured nursing assessment of a person’s physical, mental, and social abilities and needs. Nurses need to have an understanding of how to assess changes in a person’s physical and mental health, including their level of pain, distress, and ability to make informed decisions, and how this may fluctuate in different settings and across the lifespan. They also need to be alert to the risks of diagnostic overshadowing when undertaking assessments, from which they will plan nursing care in collaboration with the people with intellectual disabilities and their carer/carers.