Many popular patterns utilize double decreases – when you decrease two stitches at a time. Just like other decreases, there are different ways of doing them so they lean or align just how you want! 

Center Double Decrease (CDD)

Slip 2 stitches as if to knit, K1, PSSO

This double decrease is used a lot as a center spine to mitered squares or shawls, hat decreases, and raglan sweater decreases.

S2SK

Slip 2 as if to knit, slip1 as if to knit, hold the stitches in the front and knit them through the back loop.

This is also a centered decrease, but isn't as common as the Center Double Decrease.

Slip, Slip, Slip, Knit (SSSK)

Left leaning double decrease. This turns 3 stitches into one left leaning stitch, the opposite of k3tog.

Knit 3 Together (K3tog)

Right leaning double decrease. This turns 3 stitches into one right leaning stitch, the opposite of SSSK.