Rye whiskey was America's first and most popular whiskey before Prohibition nearly wiped out production and public demand.  Distilled from at least 51% rye mash, rye tends to be lighter, dryer, and more peppery than other types of whiskey such as bourbon or scotch.  Rittenhouse Straight Rye Whiskey is "bottled in bond" or "bonded" which, among other things, means that it must be aged in oak casks for at least four years and be minimum 100 proof.  The extra aging gives this rye complexity and depth.