Catalyst Game Labs, the current owners of BattleTech, have divided history into six eras. The products they released are grouped in this manner. Recently newer products have included other distinct time periods by splitting the eras into sub-eras which brings the classification up to nine eras. In addition to those, four more distinct non-canon ones can be identified:
|Pre-Spaceflight||Before 1950||Earliest era referenced, when humanity only resides on its planet of origin, Terra.|
|Early Spaceflight||1950 – 2005||Early solar system restricted spaceflight.|
|Age of War||Age of War (First Exodus)||2005 – 2242||The time of the Western Alliance, early Terran Alliance, and earliest interstellar colonies. The Outer Reaches Rebellion resulted in the Demarcation Declaration, the forced independence for most colonies.|
|Age of War||Age of War (Second Exodus)||2242 – 2398||Colonists on marginal worlds resettle or perish. The Terran Alliance collapses; the beginnings of the Terran Hegemony and the Great Houses of the Inner Sphere.|
|Age of War||Age of War||2398 – 2570||The time of the Terran Hegemony and "civilized" warfare between the Inner Sphere houses. The first BattleMech is created.|
|Star League||Star League||2571 – 2781||The time when the Star League reached the height of its power and was destroyed by the Amaris Coup.|
|Succession Wars||Early Succession Wars||2781 – 2900||The start of the Succession Wars, when the Successor States of the Great Houses vied for supremacy after the collapse of the Star League.|
|Succession Wars||Late Succession Wars||2901 – 3049||After years of war, many of the advances of the Star League had disappeared, becoming LosTech. Warfare between the Successor States ground down to low-level fighting.|
|Clan Invasion||3050 – 3061||The time between the beginning of the Clan Invasion and the Inner Sphere's victory at the Great Refusal.|
|Civil War||3062 – 3067||The years in the shadow of the Federated Commonwealth Civil War.|
|Jihad||3068 – 3080||The time when the Word of Blake unleashed its Jihad.|
|Dark Age||Formation of The Republic||3081 – 3130||The time from the defeat of the Blakists to the creation of The Republic of the Sphere.|
|Dark Age||Dark Age||3131 – 3150||The time since the collapse of the HPG network caused political chaos in The Republic of the Sphere that led to the militarization of Industrial Mechs and other civilian equipment.|
|IlClan||IlClan||3151 –||The once-invulnerable Republic of the Sphere lies in ruins, torn apart by the Great Houses and the Clans. As Fortress Republic collapses, the Clans race toward Terra to create a supreme authority which will rule the Inner Sphere by any means necessary.|
- Master Unit List: Battle Value, p. 2: "Era Legend"
- Catalyst Game Labs: "Classic BattleTech Eras"
- The Periphery, p. 12: "First Exodus"
- The Periphery, p. 14-19: "Beyond the Farthest Star" & "Inner Sphere Politics"
- Strategic Operations, p. 167: "Faction Quality Table"
- Catalyst Game Labs' forum: "Topic: The Republic era?"
- Record Sheets: Clan Invasion, p. 4: "Battletech Eras"