Under a lightweight, uninsulated canvas jacket in cool weather (shown in pic), or an insulated canvas jacket in cold weather. In warm weather I wear a short-sleeved button-up shirt. I either pull the shirt up with my left hand to draw, or I wear it unbuttoned with a colored t-shirt underneath. Another option I occasionally use is a somewhat loose-fitting t-shirt; this holster conceals well enough that I can wear my G19 completely concealed under a t-shirt.