Additive manufacturing (AM) technology has been attracting increasing interests in the applications of microwave antennas and components. Among a large number of AM techniques that can be categorized by methods of shaping, printing materials, etc., metallic 3-D printing is specialized for constructing structures from metal powders, and is particularly suitable for prototyping geometrically complex waveguide-based components. With metallic 3-D printing, a direct and monolithic integration of waveguide components is possible with smaller tolerances in the fabrication and assembly, and more importantly a significant reduction in the cost of time and labor. This paper presents an overview of recent advances in metallic 3-D printed waveguide-based antennas and passive components developed by the authors' group, with an outlook to future innovative evolutions in the structural design, AM, and post processing techniques.