India is the second most populous country in the world with a population of about $1.25$ billion people in $2013$. The population is growing at a rate of about $1.2\%$ each year.^[1] If this rate continues, the population of India will exceed China’s population by the year $2031$. When populations grow rapidly, we often say that the growth is “exponential.” To a mathematician, however, the term exponential growth has a very specific meaning. In this section, we will take a look at exponential functions which model this kind of rapid growth.