The causes of ill health and death are changing and, as we live longer, new health-preventable problems emerge, bringing new challenges. Improving health (physical, mental or both) and promoting general well-being remain major priorities.

Just as important, the difference in health status between rich and poor continues to grow. At a global level, the picture is even more complex. Although there is some evidence that life expectancy is beginning to plateau in developed countries such as the UK, the biggest potential to improve health still lies in addressing inequality between or within countries.

Therefore, this chapter:

• summarizes the models of health improvement that are prevalent today;

• introduces a combined conceptual model to describe the factors affecting health in modern times; and

• presents some case studies of interventions designed to improve health which offer important insight and learning.

The first element of understanding how to improve the health and well-being of a population relies on a thorough assessment of the needs of the specified population, be it a local population defined by geography, a specific age group or those with certain characteristics. This chapter begins by considering how ‘health need’ can be conceptualized; the distinction between need, demand and supply; and the difference between health needs and the need for health-care. Secondly, the wider determinants of health are introduced and their relation to health needs discussed. Finally, the steps involved in a systematic assessment of the health needs of a defined population are explained, including tools and resources used to achieve this. Practical challenges are considered.