Dieter Ram's design principles

Rams in 1969 (Picture taken from Design Museum Collection)

Good design is innovative.
Good design makes a product useful.
Good design is aesthetic.
Good design helps us to understand a product.
Good design is unobtrusive.
Good design is honest.
Good design is durable.
Good design is consequent to the last detail.
Good design is concerned with the environment.
Good design is as little design as possible.
Back to purity, back to simplicity.

From a Design Museum Collection interview with the former design head of Braun. (Picture credit: Design Museum Collection)