Why is it that my fireplace smokes my living room?

I mean it’s not like a mad smoke coming out as if it were a fire but if you flash a light to the ceiling you can catch a glimpse of the smoke hovering over the fire place. Sometimes we crack a window open and it creates a draft inward and voila, no more smoke but who wants to do that all the time? I know it has to do with atmospheric pressure (yes?) so what’s the science behind a solution? The house was kind of cold at 68d’s when we had the fire going. HELP