Technological Achievement Tiers

The Forerunners categorized the Technological Advancement of civilizations into Tiers. This system was later adopted by the Covenant. All life and civilizations in the Universe fall into one of the categories. The lower the Tier number, the more advanced the civilization's technology is/was. It should be noted that this is also a reference to Bungie's favorite number of 7.

Tier 7: Pre-industrial
Tier 7 is one of the most common and stable states, with limited weaponry and environmental threats. Societies tend to be small and scattered, driven by subsistence farming, foraging, or hunter-gathering needs. Technology is limited to simple hand made tools, weapons, or agrarian implements and methods, but a very broad understanding of planetary and solar mechanics is not uncommon.

Tier 6: Industrial Age
Tier 6 is often the pinnacle for a civilization. Agrarian societies can remain stable in the pre-industrial stage, but Tier 6 population strain and mechanized food production invariably create political and economic pressures very few can balance. Moving past this usually promises advancement. Some societies improve environmental and medical understanding concurrently with mechanical and transport advancement. Those that do not are frequently doomed.

Tier 5: Atomic Age
Tier 5 species usually become space-faring, focusing on clean energy production. The occasional belligerent species will use atomic energy for weapons, often resulting in mass extinctions. In-atmosphere craft are a hallmark, often leading to space flight.

21st Century Humanity stood at this level.

Tier 4: Space Age
Tier 4 is often the final resting place for species intelligent enough to break free from their cradle's surface only to fill the gulf surrounding it with war. Their comfort-focused technology can include medical advances.

This level is likely to be where Humanity is at the time of the Interplanetary War. This level is also where the Unggoy were before joining the Covenant.

Tier 3: Space-Faring
Species has efficient Slipspace navigation, mass drivers, asynchronous linear-induction weapons, holocrystal storage and semi-sentient AI (though their creation requires memory transfer from freshly deceased and/or flash cloning). They have had no outside influence.

26th Century Humanity stands at this level. This is also the Lekgolo civilization native tier before joining the Covenant.

Tier 2: Interstellar
The species has the ability to perform exceedingly accurate Slipspace navigation, near-instantaneous communication and man-portable application of energy manipulation. The unified state of the 26th Century Covenant stands at this level.

Both San 'Shyuum and Sangheili brought the other races of the Covenant to such a high technological level when incorporating them into the Covenant. The two primary extant interstellar civilizations were space-faring prior to discovering Forerunner artifacts - or each other - but they have not successfully reverse-engineered those artifacts.

Tier 1: World Builders
The species has the ability to manipulate gravitational forces, create AI with full sentience, fabricate super-dense materials, perform super-accurate Slipspace navigation and the ability to create worlds (e.g.; Onyx, The Halo Array and The Ark).

The Forerunners are the only known civilization to reach this level.

Tier 0: Transsentient
As the Forerunners had no examples of civilizations with technological accomplishments greater than themselves - with the exception of the Precursors - this is a theoretical ceiling. It is suspected that they can travel across galaxies and accelerate the evolution of intelligent life.