A long time ago I heard the adage that it takes something like 43 muscles to frown but only 17 muscles to smile, ergo, we should just smile because it's easier. It wasn't until my first anatomy class in college that I realized these numbers couldn't possibly be right. As far as I can tell, there are only about 36 named muscles of facial expression, and they're not all involved in smiling and frowning. Here they are in alphabetical order (a "2" in parentheses means the muscle is bilateral, "1" means it's unpaired):Auricularis anterior (2)Auricularis posterior (2)Auricularis superior (2)Buccinator (2)Corrugator supercilii (2)Depressor anguli oris (2)Depressor labii inferioris (2)Depressor septi nasi (1)Frontalis (1)Levator anguli oris (2)Levator labii superioris (2)Levator labii superioris alaeque nasi (2)Mentalis (1)Nasalis (2)Orbicularis oculi (2)Orbicularis oris (1)Platysma (1)Procerus (1)Risorius (2)Zygomaticus major (2)Zygomaticus minor (2)So which ones are responsible for smiling and/or frowning? I could hazard a guess, but I'll defer to Dr. David Song , a plastic surgeon and Associate Professor at the University of Chicago Hospitals, who was interviewed for a Straight Dope article: Does it take fewer muscles to smile than it does to frown? Counting only the muscles that make significant contributions, he concludes that smiling takes one more muscle than frowning (12 vs. 11). That doesn't necessarily mean that smiling is harder to do. Maybe it is, maybe it isn't. I suppose you could compare the masses of "smiling muscles" vs. "frowning muscles" to get a rough estimate of energy consumption (assuming the muscles all consume energy at the same rate per unit mass). In the meantime, check out Happiness Is Only Grin Deep at the always enlightening and entertaining Urban Legend Reference Pages.