Watch buyers often start with a very broad question: sport watch or dress watch?
If it's a sport watch, then the choices branch in a hundred directions like a choose-your-own-adventure novel. Clearly defined genres of sport watch include dive, pilot and motorsport watches as well as military watches and more, each seemingly with its own sub-genres. In this context, it makes sense to define a watch by its intended purpose, but this leaves dress watches — ostensibly just for "dressing up" — lumped into a single ill-defined mass despite the variety that exists.
Aside from its pragmatism and simplicity, a dress watch is primarily identified by its design and aesthetics: you more or less know a dress watch when you see it. This is subjective, of course, as watches made for action in the past may today be viewed as "dressy." There are, however, a range of different (though often overlapping) types of dress watches available, and being aware of the most common traditional styles will help any potential buyer narrow down their search.
Classical Dress Watches
If a dive watch is rock-n-roll, think of the classical style of dress watch as a string quartet playing Bach: the feel is very conservative and perhaps even of another time. Typical traits might include Roman numerals or simple stick indices, thin hands, monochromatic colorways and traditional decorative techniques like guilloche.
The minimalist approach to watch design is naturally understated and easy to fit into a dressy theme, even though it can also have a casual feel. German and Scandinavian brands seem to have a knack for this genre, as exemplified by the Bauhaus movement. Pared-back dials with thin cases can feel fresh and contemporary compared to those of more traditional watch styles.
Complicated Dress Watches
Many dress watches are characterized by simplicity, but this doesn't have to be the case. If rendered in an elegant way, dress watches can incorporate a range of complications, features and information — and this offers a whole new wearing experience. Calendar information and moon phase indicators are popular features, but even chronographs are fair game.
Rectangular Dress Watches
Square and rectangular watches were once much more popular, but today the vast majority are relegated to formal styling. The proportions are key to getting a good fit, so remember that these watches wear larger than their diameter would suggest. Thin cases also help, and when you get the proportions right the look is as classic as it gets.