Image source: Facebook.

It's not an exaggeration to say that Facebook (NASDAQ:FB) has accomplished what no other social network before it ever has. The company has reached such a critical mass of users that it has firmly established itself as the dominant social network on the planet, and by a large margin. It goes without saying that any social network relies heavily on network effects, and in this respect Facebook is unrivaled. No other social network has even gotten close to approaching Facebook's sheer size.

The Internet continues to evolve and include new phases. First, there was display, then there was search, and now there is social. Different companies embody each of these phases, and Facebook easily represents the current phase of how people interact on the Web. One of the most relevant user metrics for Facebook is how many people access the service in a given month. These users are considered monthly active users, or MAUs.

As of the most recent quarter, Facebook had a total of 1.55 billion MAUs worldwide.

Facebook users
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Considering the ongoing secular shift to mobile platforms, mobile MAUs are also an extremely pertinent metric for investors to watch. Here is a comparison Facebook's monthly active and mobile monthly active users since 2012.

Quarter

MAUs

Mobile MAUs

Q1'12

901

488

Q2'12

955

543

Q3'12

1,007

604

Q4'12

1,056

680

Q1'13

1,110

751

Q2'13

1,155

819

Q3'13

1,189

874

Q4'13

1,228

945

Q1'14

1,276

1,008

Q2'14

1,317

1,070

Q3'14

1,350

1,124

Q4'14

1,393

1,189

Q1'15

1,441

1,248

Q2'15

1,490

1,314

Q3'15

1,545

1,385

Source: SEC filings. User figures in millions.

Going forward, Facebook's user growth may slow, but what matters now is that the company continues to increase monetization of existing users.

Evan Niu, CFA owns shares of Facebook. The Motley Fool owns shares of and recommends Facebook. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.