When a star is described as a spectral class G2V, we know that the star is similar to our Sun. We know its approximate mass, temperature, age, and size. When working with an extra-solar planet database, it is very useful to have a taxonomy scale (classification) such as, for example, the Harvard classification for stars. The taxonomy has to be easily interpreted and present the most relevant information about extra-solar planets. I propose the following the extra-solar planet taxonomy scale with four parameters. The first parameter concerns the mass of an extra-solar planet in the form of the units of the mass of other known planets, where M represents the mass of Mercury, E that of Earth, N Neptune, and J Jupiter. The second parameter is the planet’s distance from its parent star (semi-major axis) described in logarithm with base 10. The third parameter is the mean Dyson temperature of the extra-solar planet, for which I established four main temperature classes; F represents the Freezing class, W the Water Class, G the Gaseous Class, and R the Roasters Class. I devised one additional class, however: P, the Pulsar Class, which concerns extra-solar planets orbiting pulsar stars. The fourth parameter is eccentricity. If the attributes of the surface of the extra-solar planet are known, we are able to establish this additional parameter where t represents a terrestrial planet, g a gaseous planet, and i an ice planet. According to this taxonomy scale, for example, Earth is 1E0W0t, Neptune is 1N1.5F0i, and extra-solar planet 55 Cnc e is 9E-1.8R1. Key words: Catalogues – Extra-solar planet – Habitable zone – Planets