An I-cord Cast On creates an I-cord edging and casts on stitches at the same time.
For each I-cord row, the first stitch is knit in the back and front[i] of the stitch; the extra stitch created stays on the right needle in subsequent rows creating the cast-on stitches from which the pattern will be worked later.
Using a Long-tail Cast On, cast on 3 (4) sts on a double-pointed or circular needle. (The sample shown is using a 4 stitch I-cord.)
Do not turn. Keep yarn to back of work. Snug the yarn as you begin each row so that the I-cord closes up in back.
*Slip 3 (4) sts to Left Needle (LN); kbf, k2 (3); rep from * until there are (3) 4 more sts than the desired number of sts on the needle. Turn.
(WS) Purling, bind off 3 (4) sts (the I-cord sts). Slip stitch remaining from bind off to the LN. Turn.
[i] knitting into the back and then into the front of the stitch tightens up the cast-on stitches preventing the loose cast on that sometimes results from an I-cord Cast On