How do big websites like Wikipedia make money, if we can use them for free?

They make money by having daily visitors. e.g They purchase google adsense and paid by google on each visitor, By displaying adds on their website and getting paid by add owners, By getting sponsors companies and also by public funding http://wikimediafoundation.org/wiki/Fund etc

I think 

number of visits

Ads                                                                        

Non-profit Organization

Donations

number of visits

Ads

Sponsors

wikipedia works on charity, anyone can contribute to it both information wise or financially

through advertisements, no of visits and clicks

We are not using for free, we are paying the government and the government also pay for the website owners.

1. Advertisement

2. Each click on the website will provide them income

Basm Allah Alrahman Alrahim

Think Like they Think ?

If you want to make something good what will happen to you and your personality ?

Wikipedia creators and GNU/Linux Creators 1 and 2 and Linux Free Distribution Creators (e.g Ubuntu Open-SUSE etc ) FOSS ( Free Open Source Software ) Creators by FSF ..etc , What Happen To All Of Them ?

They Know more than you can imagine and they are very famous and rich

So Why Don't any one think like them ? start to change your life with open source

I Forget To mention JAVA

Thank you for that interesting question

Simply they take a commission on the number of visitors per day

They get money by the number of visits and clicks on the site ,through the purchase of Google Adsense and also by paid. Adverts

Most of you said advertising yet I see ad on wikipedia page. I know wikipedia funded by donations.