A non-profit organization called Seed Saver Exchange sums up a philosophy inherent in the act of culling and saving pumpkin and other such seeds for later planting. They exist to "...save and share the heirloom seeds of our garden heritage, forming a living legacy that can be passed down through generations." Home gardeners may attain the same goals or simply save seeds from one year's crop to have free seed for the next season's pumpkin planting.
Procure a well-shaped healthy pumpkin during harvest season. Select a variety that is not a hybrid, because genetically, the seed will not create the same pumpkin as the parent; the seed will produce only one of the parents that were merged to form the hybrid source pumpkin.
Cut the pumpkin with any technique you prefer. Whether it is autumn and time to carve a jack-o-lantern or process the pumpkin meat for holiday pies and side dishes, it is the part you would ordinarily discard that you are interested in for saving seeds.
Remove as much pulp from the seeds as possible, and then place the seeds into a large bowl or pan of water. Continue to work the seeds with your fingers in the water to remove as much pulp as possible. As the seeds move free of the pulp, move them to a screen strainer set over another bowl to catch the moisture and allow the seeds to start air-drying while you finish the batch. Allow the seeds to dry thoroughly on paper towels, which should take two or three days. It is best to remove them to a clean, non-windy, low-traffic area as not to be disturbed during this process.
Seal the dried pumpkin seeds within an envelope after they are completely dried. Do not include any marred, molded or broken seeds to keep your batch as healthy as possible, so they may result in a hearty crop for for your next season's planting.