It took hundreds of thousands of years for the world population to grow to 1 billion and then it grew seven times in just another 200 years or so. The global population reached the 7 billion mark in 2011 and it is all set to cross 8 Billion this year. This number is expected to grow to around 8.5 billion in 2030, 9.7 billion in 2050, and around 11 billion in 2100. This dramatic growth has been driven largely by increasing numbers of people surviving to reproductive age, major changes in fertility rates, increasing urbanization and accelerating migration. Around Sixty-one per cent of the global population lives in Asia with China and India being the two most populous countries of the world. In fact India is projected to overtake China by 2027 in terms of population numbers. More than half of global population growth between now and 2050 is expected to occur in Africa. However the populations of 55 countries in the world with most of them in European continent are expected to decrease by 2050, of which 26 may see a reduction of at least ten per cent.