Wash the jalapeños and pat dry.
Decide if you want the peppers frozen whole, sliced, or diced. Most recipes call for sliced or diced jalapeños, unless you're making poppers or stuffed peppers.
Trim off the stems. If freezing the peppers whole, use a paring knife and spoon to cut out the membrane and remove the seeds. For sliced jalapeños, perform this step then slice them crosswise into circles. If freezing them diced, cut them in half lengthwise, then remove the membranes and seeds. Cut the halves into strips and then into diced pieces. Alternatively, you can leave the seeds and membranes for more heat if desired.
Place the peppers (whole, sliced, or diced) into freezer-safe bags or containers. I usually recommend reusable silicone bags, but here I suggest plastic bags or glass (freezer-safe) containers. This is because jalapeño can rub off on silicone and be hard to remove, so I like to prevent any lingering jalapeño on containers I use for other foods.
Seal the bags or containers tightly and label. Store them in the freezer for up to 6 months. If using bags, I like to lay them flat and spread out the jalapeños into a single layer so they don't freeze in clumps.
Add frozen jalapeños directly to recipes without thawing first. They work great in soups, casseroles, and other cooked dishes.