In 3132, eighty percent of the hyperpulse generators in the Inner Sphere shut down, silencing virtually all interstellar communications between the thousands of worlds humankind called home. Remembering the horrors of the Jihad that ended just half a century before, paranoid citizens and opportunistic leaders across the Sphere instinctively girded for the invasions that were sure to come. As ancient rivals once again turned against each other, the Republic of the Sphere - once a beacon of hope for billions - found itself nearly torn asunder by hostile neighbors on every side. A new Dark Age had begun. Era Report 3145: describes the state of the Inner Sphere at critical age in BattleTech history: the years of the Dark Age era. Presented as a general overview of the period, rather than a focused report on a single conflict, this book includes descriptions of every major Inner Sphere faction active in the wake of the catastrophic failure of the interstellar HPG grid. Notable personalities, military forces, and an overview of the technological capabilities of the Dark Age era are also provided, along with special advanced-level rules for campaigns set during this time, whether played using the Total Warfare core rules or those found in A Time of War: The BattleTech Role-Playing Game.