Intarsia is a flat knitting technique in which there are blocks of color large enough that other colors cannot be stranded behind the work. Each block of color is knit with separate small amounts of yarn, usually kept on bobbins. As each color change comes up, the new color is picked up from under the previous color, twisting the strands so there is no hole in the knitting. Here is the front of a pattern I just started working with 3 colors of sock yarn:
Now for the scary part (the back of the work with all the strands of yarn:
This pattern is "Garden Trellis Argyle" from Alice Curtis' book, Knit Your Socks on Straight. This book has 20 patterns for 2-needle socks made flat and seamed with a crocheted slip stitch. It's another interesting way to make a sock. Stay tuned as this project begins to take shape--literally!
Intarsia is most famously used in making argyle socks (another thing on my to-do list) and is also used for sweaters with a large motif. I find intarsia more demanding than fair isle knitting, because I dislike purling with more than one color (although I will knit with multiple colors all day long!)