This page currently concentrates on difference between the rich and poor in the US. There are many other types of income disparity, e.g. gender and race differences, developing and developed countries, regional differences, ...

Income:

Source: New York Times article "Two Candidates, Two Fortunes, Two Distinct Views of Wealth" (Romney and Edwards), Dec. 23, 2007

The top one percent of households received 21.8 percent of all pre-tax income in 2005, more than double what that figure was in the 1970s.

In 1979, the average income of the top 5 percent of families was 11.4 times as large as the average income of the bottom 20 percent. In 2005, the ratio was 20.9 times. (EPI, State of Working America 2006-07.
Source: By the Numbers inequality.org

The ratio of the compensation of CEOs to the average worker in 1974 was 35 to 1; in 1995 it was 150 to 1.

Wealth (assets):
The inequality in wealth is even greater than that of income.

In March 2006 Forbes reported 793 billionaires in the US with combined net worth of $2.6 trillion. In March 2007 Forbes reported 946 billionaires in the US with combined net worth of $3.5 trillion. That is a 1-year increase of 19% in the number of billionaires and an increase of $35% in their net worth during a time of increasing poverty. Severe poverty is at its highest point in three decades.

Household distribution of net worth (1998), i.e. total value of assets:

Percent of owners	Net worth	Cumulative Percent	Cumulative net worth
Top 0.5%	25.6%	Top 0.5%	25.6%
Next 0.5%	8.4%	Top 1%	34.0%
Next 4%	23.4%	Top 5%	57.4%
Next 5%	11.4%	Top 10%	68.8%
Next 10%	12.8%	Top 20%	81.6%
Last 80%	18.5%	All 100%	100%

Source: LCurve.org