1. Flat-panel door style
This is sometimes referred to as a slab-door style and is a signature element of modern kitchen design. You might see a modern kitchen using a Shaker door style, but that often falls into transitional rather than modern — which is not to say it can't be used; it's just not a purist's perspective.
2. Frameless, full-overlay cabinet construction
A bunch of terms are thrown around to describe this type of cabinet construction: frameless, Euro frameless, overlay, full overlay. They all mean the same thing, that the door overlays the cabinet box. This style is the most often used in modern kitchens because it's sleeker than a flush-inset cabinet, which is often associated with more traditional kitchen, cabinet and furniture design.
3. Sleek and simple hardware
In modern kitchens you'll most often see C-channel hardware that's integrated into the cabinet, as well as tubular pulls or flat linear pulls. Lots of times the horizontal lines of the cabinets will be accentuated by cabinet hardware running the full length of the drawers and doors.
4. Lack of ornamentation
Always a signature of modern, this is often where contemporary and modern stop being similar. Whereas you might see patterned tile shapes or multiple materials with texture, color and patina in a contemporary kitchen, you won't see much of that in a modern kitchen. Flat-panel door styles and sleek hardware are joined here by a simple full-height glass backsplash and countertops without any pattern or veining.
5. Reliance on the beauty of natural materials
It's not to say that modern kitchens can't have a little bit of ornamentation, but when they do, they get it from the natural characteristics in a material, such as the horizontal grain of oak when it's rift cut or the natural beauty and veining of marble.
6. Consistency in style of accent pieces
Accents like lighting, tables, chairs and bar stools all have to be considered when designing a kitchen. In a modern kitchen these elements will stay consistent rather than deviate like you'd see in an eclectic kitchen.