Stretchy Slipknot Cast-On, by Jeny Staiman

I came up with this technique on my own when I was in college, then later discovered that it's been around for awhile. I think many knitters have had this experience. :) Some have told me this is a Russian technique, others say it is Estonian... in any event, it is simply slipknot after slipknot.

This cast on is fantastically flexible, but it can admittedly be a pain to do. Each stitch has two structural elements: (1) loop, (2) yarn wrap, and the wrap is pulled through the loop. As you tighten each stitch, the working yarn has to slide through a tight space, so the technique works best with smooth, slippery yarn (e.g., superwash sock yarn). I don't advise using this technique with yarns that are highly textured or that vary in thickness.

You can vary the direction of either of the two structural elements:
the loop can be backward or forward (this video shows a backward loop).
you can wrap from front to back or back to front (this video shows front to back). In the time since I posted this video, I've discovered it's a little easier to tighten if you wrap the yarn the other way (see Janel Laidman's video, linked below)

A few references:
1. My friend Janel Laidman's demo video at    • Janel Laidman's slipknot cast on  
2. Hands Occupied's version:    • How to Work Jeny's Stretchy Cast On i...  
3. "Knitter's Handbook" (1993) by Montse Stanley; this technique is called the "Buttonhole Cast On" in this book. This is the oldest publication of this technique that I'm aware of.
4. Leslie Ann Bestor's book "Cast On, Bind Off" (2013) contains a photo tutorial that matches this video.