Total Immersion swimming

Many people have had good experiences with TI swimming. I used it myself back in 2006 for my first Ironman and credit it with swimming success.

It is a set of videos plus workshops that cost a few hundred dollars.  There is a certified TI instructor that frequents this board and she can explain more (AdventureBear, real name Suzanne Atkinson).  I notice the links to other posts below are really ancient.  Here's a much better one with comments from Suzanne.

http://www.beginnertriathlete.com/discussion/forums/thread-view.asp?tid=538951

Swimming cannot be book learned and videos only go so far.  Personal direct instruction is necessary. I compare swimming to playing the piano. It's not "training" it's "practicing" and if all you do is play the wrong notes over and over (akin to having a poor swim technique) then there is no way you will get better.  Worse, you will have to unlearn bad habits you didn't even know you had.

if you want to learn how to be a mediocre swimmer, its the program for you.

It's very good for new swimmers. The drills are excellent for new swimmers.

It oversells itself however on the 'swim easy and go FAST' claims it repeatedly makes in the book. The books makes you think that by decreasing your drag in the water, you'll become a FOP swimmer, which is patently false - you need both drag reduction AND propulsion to go fast.

And the only way to improve propulsion is to swim hard, and a lot. No shortcut.

LMAO!  That's some funny stuff!  You realize that you're telling one of the top coaches in the TI teaching methodology that she doesn't look like a TI swimmer.  Maybe that should make you step back and reconsider what you think you know about TI.

There's no such thing as TI swimming.  There's a lot of bad advice that pops up every time a TI thread is started. The most common ones are predicated on the misconception that TI is a way of swimming. So, comments like "it'll make you slower" or "it's a good way to become a mediocre swimmer" are made by people who don't understand it.  It's an excellent methodology for swimmers of every ability level. Don't be dissuaded by people who don't actually know anything about it,  nor clips from learning videos intended for beginners. What is shown in those types of videos has very little resemblance to what a coach like Suzanne does with a more advanced swimmer. 

Hence my statement that you should rethink what you think you know about TI.  You say you don't understand how it differs from conventional freestyle.  That's because it doesn't.  Fast swimming is fast swimming. The difference is just in how areas for improvement are identified and changes implemented.  The objectives are the same as any other methodology: fast swimming with energy conservation via reduced drag, increased lift, and increased power production.  If you think Suzanne has poor balance in the water, and the only thing you pick out of those videos is that they seem to have a slower stroke rate, then you may also want to reconsider your assumptions regarding what makes an athlete a fast and energy efficient swimmer.  One resource I like is Jim Gourley's book "Faster: Demystifying the Science of Triathlon Speed ".