The simplest way to define ecological footprint would be to call it the impact of human activities measured in terms of the area of biologically productive land and water required to produce the goods consumed and to assimilate the wastes generated. More simply, it is the amount of the environment necessary to produce the goods and services necessary to support a particular lifestyle.
What is Ecological Footprint?, with its theme of 'Protecting our home', offers a number of resources to understand and study the concept of ecological footprint. Together with Redefining Progress, it measures how much is needed to produce the resources we consume and dispose of our waste.

EF: A measure of sustainability
An interesting way to look at ecological footprint is how much nations consume versus how much they actually have. Another detailed look at the concept and a ranking of countries can be found here.

What is your Ecological Footprint?
Everyone of us has an ecological footprint. To find out how far you have put your foot in it, try this site, irrespective of your geographical location.

Ecological Footprint of 52 countries
Another way to measure ecological footprint is a country-wise ranking. Fifty-two nations are ranked here depending on how they fare in this department.

More resources
The Global Footprint Network coordinates research and develops methodological standards for decision makers to have resource accounts to ensure that we live within the Earth's 'budget'. Here is where you can find more about this.

The Redefining Progress website also offers a number of interesting resources explaining how selfish and unthinking we can sometimes be towards the environment.
Footprint made of leaves 
© iStockPhoto / Dena Steiner
Footprint made of leaves
© iStockPhoto / Dena Steiner