If you've torn your favorite pair of jeans and would rather not sport a hole, they can usually be repaired without using a patch. The direction and size of the tear, as well as the fabric, will determine how you stitch the rip. If your jeans are cotton, they'll be easier to repair than jeans made from stretch fabric which may not hold a repair as well when it gives.
Assess the Tear
If the tear in your jeans is against the seam or goes with the grain of the fabric, it will be a fairly easy fix. If the rip is against the grain, it will be more difficult to hide the repair and you might want to consider using a patch. If the tear is due to wear and the fabric is thin, a patch might be needed. However, you can use a patch and still keep the repair invisible.
Stitch to Fix
If you're working with a tear that goes with the grain of the fabric, you can repair it with a needle and thread. Use a strong, heavy-duty needle for cotton denim. It will be easier to work through the thick fabric. Stretch denim is thinner and easier to sew through. Turn the jeans inside out and cut the excess threads away from the tear. Match your thread to the color of the jeans. Pin the tear together, leaving just enough overlap to sew through securely. If your jeans are stretch denim, use stronger thread and leave a bit more fabric when you pin the tear together. The fabric needs to be able to stretch, and a repair can pull out more easily after it's sewn.
Begin at one end of the tear and take one stitch through the material. Knot that end of the thread. Continue down the length of the tear, using small stitches that are close together. This will ensure that your repair appears seamless and doesn't show. When you reach the end of the tear, double back with another set of stitches so you end where you began. This will result in a strong repair that will stand up to the wear and pulling your jeans require.
If you're an experienced sewer and have access to a sewing machine, you can repair the tear using the same basic method. With the jeans inside out, make a small hem at the tear and trim off excess thread. Thread the machine with a color that closely matches the jeans' fabric, and do a single row of stitching up and down the hem, for an even, seamless repair.
Use a Patch
If the rip in your jeans is large because of fabric wear, or has created a hole, you might need a patch. If you don't want the patch to show, use material that matches your jeans. Turn the jeans inside out. Measure the tear and cut the patch, rounding the corners to prevent unraveling. The patch should be roughly one-half inch larger than the tear. Pin it in place and check to ensure it isn't puckered. Baste the edges and stitch a single row around the patch with a sewing machine. Go over the edges again with a zigzag stitching pattern for additional strength.