This is an awesome jacket that I initially struggled over ordering b/c I was unsure of sizing and fit. I am writing this review to help someone torn btw getting the SML or MED. For reference, I am 5'4", 130-135 lbs with a 34DD/E bust, long arms, narrow shoulders and hips. Jean size 27. Reading other people's reviews, I was surprised how many people have very similar, to exact, dimensions as me, yet how differently we all may want the jacket to fit depending how we plan to wear it. As a 52-year-old-post-partum-middle-aged-chick, I was looking for a narrow streamlined fit that would not add any bulk whatsoever to my frame. Also, I live in SoCal and did not plan to wear this over anything other than a tshirt, blouse or very thin dress or sweater. Also, I would wear this jacket totally open and unzipped 97% of the time, so I got the SMALL. When it is zipped and buttoned up all the way, the SMALL on me is a tight, but not binding, streamlined, almost a 1960s Mod Squad look. Truly fits like a glove and sleeve length is perfect. Had I ordered the Medium, I would have felt obligated to wear the jacket closed, over layers or a big sweater or hoodie; because totally open and unzipped, the front panels of the Medium would have hung and flapped around my body excessively (if that makes sense) and the shoulders would have drooped/been oversized, rounded, like a slouchy, casual 1990's fit. My teen daughter who is 5'8 and a size 0-2 (so, a human clothes hanger) would probably get this very same jacket in a Medium or even a Large because she likes that oversized look, and can carry it off really well. I hope this review helps someone else with my proportions. I may order one in a MEDIUM in case I ever want room to really bundle-up with lots of other layers or a really thick sweater for much colder weather. But, I think if that happened I would just wear a longer coat to stay warm. Either way, it is a great purchase.