Almost everything we do today generates data. We can learn a lot about ourselves by tracking that data. In the past this type of data-collection was possible but difficult, but today capturing data about ourselves is often trivially easy.

Self-tracking is not new. We kept track of our weight or other metrics by writing it down. Today we can measure and record those kinds of things much easier, more precisely and sometimes automatically — like using a scale that transmits our weight to a spreadsheet wirelessly, or wearing an always-on glucose meter.

Because tracking our data is so easy, more and more folks are doing it. Some people track only one thing at a time; a few track several variables and a very few track dozens and maybe hundreds of factors in their lives. I’ve been calling this habit the rise of the quantified self. The idea has grown steadily and I thought I’d provide a status update on this meme.

About three years Gary Wolf and I put up a notice on Meetup to see if anyone who was quantifying themselves would like to come to my office to talk about it. Twenty five showed up. We’ve been meeting about every two months since then, and more and more folks show up. Last night we held the 18th Bay Area Quantified Self User Group Meetup. We had 150 people stuff themselves into the San Francisco Techshop great room, and we turned away another 100 people on the waiting list.

We are just one of many groups gathering to show and tell about the tools and techniques users have discovered or invented to self track. More than 20 cities around the world now have Quantified Self meetup chapters. Like the group in New York (below) they meet to swap tips and insight on the methods they are using, or to get feedback on a tool they are making themselves.

The number of members is growing rapidly just in the last 9 months (see chart below).

And so are the number of companies that we have identified as selling tools or services in the general area of self-tracking. (Both these charts were compiled by Alexandra Carmichael, who is director of Quantified Self Labs, the tiny organization currently serving as a clearinghouse for self-tracking information.

So there are all these people very nerdily tracking themselves and downloading piles of data about themselves. Why? What are they learning? Is it worth the trouble? And should I be doing the same? Or is this the high-mark of narcissism and decadence, the end of civilization as we know it?

Those are big questions and Gary Wolf, a contributing writer at Wired, is hoping to answer some of them by writing a deep book about this frontier. In the meantime, here is my summary of what I’ve learned about self-tracking in the past three years. (To be clear, I am not much of a self-tracker myself; I am reporting what I have learned about other self-trackers and the quantified self movement as a whole.)

* There is no end to what can be, and will be, tracked. At each QS meeting I am surprised and amazed at the unpredictable qualities that people will monitor and the clever ways in which they will attempt to quantify them. We’ve seen one person (or more) track one (or more) of these: sex, dates, attention span, REM sleep, car routes, daydreams, caffeine intake, people they meet, every keystroke, arithmetic speed, allergic reactions, mood, happiness, footsteps, memory recall, body motion, and every medical and health related factor one can quantify. Also check out the lifeloggers.

* There is no end to folks hoping to make a better tool to sell to self-trackers. Like the early days of personal computers, most of the tools available now are primitive and often first cobbled together by someone for their own use. That’s what makes the groups so interesting. But as what works and what is desirable settles out, slickness will move in. There’s lots of money watching.

* Collecting data is easy. Quantifying not so hard. The great challenge is making sense of the data. What should one pay attention to? How do you extract out meaning from 25 variables? How does one turn data into actionable differences? One of the mantras around Quantified Self is that obsessive self-trackers may look outrageously geeky now, but they will soon be the new normal. I think this is one reason to track the self-trackers: because we all will be living in an ocean of data n the near future, whether we are self-tracking or not, and learning how to read, manage, retrieve, understand, digest, parse, and selectively ignore this flood of data will be an essential skill – for individuals and for organizations. Self-trackers are there first.

* Self-tracking breeds self-experimenters. More and more of health care will depend upon, and often be reduced to, self experimentation. We see this already. People use cheap tools to measure themselves, and begin to isolate variables to test for influence in order to alter their behavior. Clinical trails of one will not be unthinkable.

* Self-tracking often quickly becomes peer-tracking. In health related monitoring, the addition of others who are also self-tracking similar factors, or diseases, or treatments, can exponentially increase the vale of tracking for all. Often self-tracking becomes co-tracking with peers. And with peers, learning accelerates. It is no coincidence that Quantified Self director Alexandra Carmichael is also founder of CureTogether. These adhoc experiments in collective self-experimentation open up a very tiny frontier in the scientific method.

* Identity is our mystery. We have no idea who we are – what humans are, and what humans are good for. What it means to be male or female. What it means to be an American or Chinese or French is all in flux. On facebook where do we end and our friends’ identity begin? Are we machines or something spiritual, or even supernatural, something unmeasurable? Self-tracking and the quantified self movement are contemporary probes into this mystery, part of our feeble attempt to figure out who we are — as individuals and a collective. Quantifying your self is an act of self assertion. All this attention is not a narcissist adoration of the self, but a self-definition in an age of great uncertainty about who we are.

That’s why I am showing up. I don’t know where this will all lead to, but it seems important. To harness the great attention this edge is receiving, the next Quantified Self meeting will be a larger-scale conference in Mountain View, CA, on May 28-29, at the Computer History Museum. There’s room for 400 at attend, and I believe there are about 60 seats left. We’ll be back to our smaller scale user group meetups in July. Or better yet, start your own local Quantified Self user group. Here’s how-to.