M-class planets, or Minshara-class planets, as the Vulcans call them, are planets found in the habitable zone of star systems. Their atmosphere contains oxygen and nitrogen and various other trace elements. The surface of these planets is made up of continents and often large bodies of water, which, however, do not occupy more than 80% of the surface. They are the bearers of life in various forms and variations, from lush vegetation, through many species of animals to the intelligent life that has evolved in many of them.

M-class planets are best suited to humanoid life, and most of them allow large parts of known humanoid species to survive without supportive means. However, individual M-Class Planets may differ radically in climatic conditions on their surface. Examples are cold Andor, mild Earth and hot volcano without large areas of water.

If water covers more than 80% of the surface, the M-Class Planets become P-Class or O-Class Planets.