Rinse the lentils and remove any stones. Place them in a jar or bowl and pour in enough water to cover the lentils by at least 2 inches. Let them soak for 8-12 hours.
Drain the water and place the lentils back in the jar and cover with a sprouting lid or a mesh cloth and tilt the jar so that excess moisture can drain out. I
The next day, little tails will have already formed. Run water into the jar rinse the lentils and pour out the excess water. Tilt again.
Continue to rinse and drain them twice a day until the sprouts are your desired length. I usually let mine go 3-4 days.
When the tails are your desired length, spread them out on a paper towel lined baking sheet until they are dry. Store in a lidded container in the fridge for up to a week.
Notes
For best results use small black, green, or de Puy (French) lentils. If you are going to cook the lentils, just sprout them for about a day, until the tails just form. For eating raw, I like to let the tails get longer, more like regular sprouts.