The Human Development Index (HDI) is a tool used to measure the progress of countries in terms of human development. It is a composite index that takes into account three key indicators of human development: life expectancy, educational attainment, and standard of living.

The HDI was first introduced in 1990 and has been updated every year since then. The most recent HDI rankings were released in 2018. In the 2018 rankings, Norway was ranked as the country with the highest HDI, followed by Switzerland, Australia, Ireland, and Germany.

The three indicators that make up the HDI are life expectancy, educational attainment, and standard of living.

Life expectancy is a measure of how long a person can expect to live. The higher the life expectancy, the better the health of a population. This is calculated by taking the average life expectancy of a population and subtracting the infant mortality rate.

Educational attainment is a measure of the level of education that a person has completed. The higher the educational attainment, the more likely a person is to have access to good jobs and to be able to participate fully in society. This is calculated by taking the adult literacy rate and the combined primary, secondary, and tertiary gross enrollment ratio.

Standard of living is a measure of the material conditions of a person's life. It takes into account factors such as income, housing, and access to basic services. The higher the standard of living, the better the quality of life. This is calculated by taking the GDP per capita and adjusting it for inflation.

The HDI is a useful tool for measuring the progress of countries in terms of human development. It is important to remember, however, that the HDI is only one way of measuring development and that there are many other factors that contribute to a country's development.