What is a Control Account?
A control account is a management point on the WBS where scope, budget, actual cost, and schedule are integrated and measured — the level where earned value is actually calculated and a named control account manager answers for variance. Work packages roll up into it; performance reporting rolls out of it.
It's a granularity decision: control at every work package and you drown in noise; control only at project level and you're blind. Control accounts are the deliberate middle.
Worked example
A shipyard structures a frigate build with 40 control accounts — "hull section 3," "combat systems integration" — each with a manager, budget, and monthly EV analysis. When CPI drops at the project level, the review doesn't start with 4,000 activities; it starts with the three control accounts driving the variance, and their managers already know why.