You do, unless you are below the age of 14. Whatever your particular fishing pleasure, licenses pay the considerable costs of keeping abundant fish in Idaho waters. Also, there is a hooking mortality on released fishes, so the angler is indeed affecting the population even if all fish are released.One of our officers added this: Idaho code 36-201 definitions says" fishing means any effort made to take, kill, injure,capture, or catch any fish .." And furthermore, "take means hunt, pursue, catch, capture, shoot, fish, seine, trap,kill ...or any attempt to do so". And finally, 36-401 says "no person shall ...fish or take... any ..fish without first having procured a license." So this is the legal reason. And also, law enforcement and resident hatcheries are totally and solely funded by license dollars, steelhead and salmon hatcheries are partially funded by steehead and salmon permits. So even when you are enjoying catch and release fishing you are enjoying the fruits of our labor and can and should expect to get checked by a representative of Fish and Game to insure a future with a healthy fishing opportunity.