The vast majority of prisoners have several health needs which combine at different levels of severity. This complexity of needs often amalgamates to include mental and physical illnesses, homelessness, unemployment, and drug and alcohol addictions. 'Complexity' can serve as an umbrella term for a number of health and social justice agendas, including public health, primary and secondary care, and social care, and must be fully understood to meet the 'complex needs imperative' that exists in all prisons.