The 100-day integration playbook: twenty-six steps, and who owns each one.

The close is a communication event before it is anything else. Everything in this group happens inside the first 24 hours.

• Announce to both companies within hours of close. Same message, same day. Nobody on the acquired team should learn the terms from the press.CEO
• Name a single integration lead with a direct line to the deal sponsor. One owner, not a steering committee.Sponsor
• Freeze system migrations and access changes for the first week. Nothing merges or shuts off before the inventory exists.IT
• Confirm payroll, benefits, and expense reimbursement run unchanged on both sides. A missed paycheck undoes a quarter of goodwill.CFO
• Call the top ten customers personally before the announcement reaches them another way. Named voice, direct number.CRO

Nothing structural moves yet. This week exists to stop value from leaking and to record how both companies work before integration changes them.

• Build the retention list: the 20 to 30 people whose departure would break operations, customer relationships, or institutional knowledge. Rank by communication centrality, not title.CHRO
• Give every account with material revenue a named owner who can fix problems without escalating.CRO
• Stand up shared channels and standing counterpart meetings between the two companies. Cross-boundary communication does not start on its own.Integration lead
• Record the baselines in both companies: who talks to whom, response latency, decision cycle time, release cadence. Convergence can't be measured without a starting point.Integration lead
• Publish the decision framework: which calls stay local, which are joint, who breaks ties. Most day-60 paralysis traces back to skipping this.CEO
• Inventory contracts with change-of-control clauses and notify counterparties on the schedule each contract requires.GC

Connection is engineered, not hoped for. By day 30 the easy wins are done, and the boundary either starts dissolving or starts hardening.

• Pair people from both companies on live projects with real deadlines. Paired work builds more cross-boundary ties than any offsite.Function leads
• Staff integration working groups at the working level from both sides. Integration that happens only between executives is coordination, not integration.Integration lead
• Measure the cross-boundary share of communication: the fraction of messages and meetings that cross the old company line. It should rise week over week from here.Integration lead
• Count the bridges. If cross-company traffic routes through fewer than five people, the connection is brittle and one resignation can sever it.Integration lead
• Re-screen the retention list for withdrawal signals: shrinking network reach, slowing replies, fading cross-boundary participation. These appear four to eight weeks before a resignation letter.CHRO

Days 30 to 60 decide the integration. This review is where behavioral evidence overrules the milestone tracker.

• Hold the formal review. Is cross-boundary communication still climbing, or did it plateau after the kickoff spike? A plateau near 10% of total volume is the classic silo signature.Sponsor
• Hunt for parallel decision-making: duplicate meetings on one topic, separate threads reaching separate conclusions. Two decision systems means the org chart merged and the company didn't.Integration lead
• Time the cascade. When leadership decides, does the decision reach both legacy organizations at the same speed? Asymmetry reads as favoritism, and people act on the reading.CEO
• Check for one-way adaptation. If only the acquired side is changing how it works, that is assimilation, and it precedes talent loss.CHRO
• Watch customer-facing response times. Slower replies to customers mid-integration are the earliest churn warning you will get.CRO

The hundredth day produces a verdict grounded in the week-one baselines. Not a status deck.

• Deliver a verdict, not a status update: integrating, stalling, or diverging. Milestone completion is not the test. Behavior is.Sponsor
• Score the verdict against the week-one baselines: communication convergence, decision cycle time, release cadence, customer engagement.Integration lead
• If converging: retire duplicated meetings, hand governance back to line management, and commit the synergy capture schedule.CEO
• If stalling: name the specific functions where the boundary persists and assign targeted interventions. Company-wide programs fix nothing specific.Integration lead
• If the behavior says the original synergy assumptions will not hold, reset the timeline with the board now. A revised plan beats a defended fiction.Sponsor