I purchased these to try to fit the niche of a winter running/cross country skiing pant. I could not be more pleased with the quality and functionality of this piece. They fit perfectly over a pair of mid weight capilene bottoms for cross country skiing. Also the zipper on the bottom firts well over my backcountry ski boots. When running, they are not too baggy and the form and fit feel great. I am 5'9" tall with a 34 inch waist and the medium seems to fit perfect. Any larger waist than that and you would probably want to consider the large. I have been cross country skiing in these as low as -10 degrees Fahrenheit and running at as low as 2 degrees Farenheit and the temperature regulation was perfect.