The first 90 days of a client relationship determine whether that client becomes a long-term partner or a one-project churn statistic. Yet most service businesses have no structured plan for this critical window. They improvise. They react. They hope it works out. This article lays out a complete 90-day client onboarding roadmap — six phases, from pre-onboarding prep through transition to ongoing service — with specific tasks, timing, and communication templates for each phase. It includes a free, downloadable roadmap template with 30+ action items and 6 ready-to-send email templates you can customize for your business today.