With the exception of the Chinese Water Deer, which have tusks, all male deer have antlers. Sometimes a female will have a small stub. The only female deer with antlers are Reindeer (Caribou). Antlers grow as highly vascular spongy tissue covered in a skin called velvet. Before the beginning of a species' mating season, the antlers calcify under the velvet and become hard bone. The velvet is then rubbed off leaving dead bone which forms the hard antlers. After the mating season, the pedicle and the antler base are separated by a layer of softer tissue, and the antler falls off.
The majority of antler I use in crafting pens is white tail deer antler obtained locally but I also have mule deer and roosevelt elk antler. Most of it is seasonally shed antler.