How do companies like Quora and Stack Overflow make money?

Stackoverflow and Quora have Ad based revenue models, but inherently different.

Quora relies on textual Ads interleaved in the content screen, the Ads are of variety of services/goods.

On the other hand, StackOverflow Ads rely solely on Job listings. The content and intelligence for Job listings is created through activity of members on StackOverflow intersected with available job listings. Example:

The Ads take you to dedicated Job search portal of StackOverflow.

The dedicated business site where users buy listing slots is Stack Overflow Talent - Hiring Developers | Stack Overflow . All the plans

Stackoverflow and Quora have Ad based revenue models, but inherently different.

Quora relies on textual Ads interleaved in the content screen, the Ads are of variety of services/goods.

On the other hand, StackOverflow Ads rely solely on Job listings. The content and intelligence for Job listings is created through activity of members on StackOverflow intersected with available job listings. Example:

The Ads take you to dedicated Job search portal of StackOverflow.

The dedicated business site where users buy listing slots is Stack Overflow Talent - Hiring Developers | Stack Overflow . All the plans are paid and start from a good enough value to generate steady revenue for StackOverflow .

Stackoverflow could also be earning by providing dedicated discussion streams, like for Facebook developer platform : Newest 'facebook or facebook-graph-api' Questions , but those would be special cases of tie-ups and not primary revenue model.

For now,

Quora : It is primarily working via it's funding money. But recently it has started showing some advertisements​ at the bottom of the answers through which it may be earning good amount of money. These advertisements are designed by Quora itself unlike other websites which use Google AdSense.

Stack Overflow : If you have ever visited this site, you can easily encounter the great number of ads it shows, sometimes at the bottom of the screen and at times beneath the answers itself. These ads are powered by Google AdSense, which displays relevant ads based on your user profile or cookies.

Questions

Ads.