It's bound to happen to any piece of clothing that a button will fall off. It can be a nuisance to deal without, but is a very simple repair that anyone can do with simple tools (that I got for free!). Hopefully this instructable will help you with any future button repairs!

Step 1: Supplies

In order to repair your missing button, you'll only need a few things!

a button (this can be the same one, or a different one)
A sewing needle that fits inside of the holes in your button
about 2-3 feet of thread (this is more than you'll use, but it's nice to have extra)
scissors

It should be noted that I got a free sewing kit at a hotel and it came with needles already threaded and 2 buttons! So I did this instructable for a grand total of $0!

Step 2: Prepare Your Needle!

Start off by threading your needle. If you're having trouble with this, there are a few tricks.

Lightly wet the end of the thread and twist any stray fibers together. Try threading this through the eye of the needle.
Using your scissors cut the tip of the thread at a 45 degree angle and try threading this through the eye of the needle
If you have an extra finicky needle and thread, there are also needle threaders (I don't have one so I can't detail how to use it), or just get someone else to try!

Once your needle is threaded, grab the two ends of your thread and pinch them together. This will scoot your needle to the center of the thread. Tie a double knot in the end of your thread to keep the two strands together.

Step 3: Start Sewing

Now you are ready to start sewing. Locate exactly where you want your button to be and begin by piercing through the back side of the fabric so that your needle comes out where you want your button to be. Once the needle makes its way through the fabric, place your needle through your button and gently pull the thread taught. The double knots that you placed in the end of your thread should keep the thread from slipping through your fabric as you continue working, but there's no need to pull especially hard.

Step 4: Criss-Cross!

Now that you have your thread through one of the holes in your button, bring your needle back and poke through the opposite hole and your fabric. You'll see that you've created a nice criss cross pattern! Move to the other set of holes and repeat the entire criss-cross 2-3 more times.

Step 5: Wrap It All Up!

Now that you've got a solid criss cross going, move the needle from the back of your shirt to the front but don't bring it through the hole. Wrap the thread a couple of times around the back of the button (to bring the criss-cross thread together, and finish it off with a nice double knot.