Australia's population has increased each year since the end of World War II due to a combination of high post-war fertility and high levels of migration.
In 1901, 23% of Australia's population was overseas-born. In 1947 the proportion of the population born overseas had declined to 10%. The creation of a national government immigration portfolio in 1945 accompanied a gradual increase in the proportion of overseas-born Australians and by 1992 this proportion had increased to 23%. In 2002 the number of overseas-born Australians had passed 4.5 million, remaining at 23% of the total population.
The diversity of countries of birth has increased substantially over the years. Patterns of immigration have also changed. For the last few decades, the Italy, Greece and Netherlands-born populations in Australia have been declining. The major migration flows from these countries occurred immediately after World War II and there has been relatively little migration from these countries more recently.
The 2001 census showed 26% of persons born in Australia had at least one overseas-born parent, that is, they were second generation Australians. Of Australian-born children with at least one overseas-born parent 43% had both parents born overseas, 35% had their father born overseas and 22% their mother born overseas. The variety and size of second generation populations reflect past migration and intermarriage patterns.
http://www.about-australia.com/facts/demographics/
http://www.australia.com/about_australia/facts_and_figures/people/Facts2_ALL.aust?L=en&C=US