This document provides an overview and key concepts from a lecture on building subscription-based businesses. It discusses recurring revenue, lifetime revenue modeling using different approaches, and the core subscription business model of acquiring new customers, boosting revenue per customer through upsells and cross-sells, and reducing churn. It also covers important subscription health metrics like magic numbers, retention rates, recurring profit margins, and growth efficiencies. A case study from SendGrid reviews their use of metrics like monthly recurring revenue, customer counts, customer retention, customer acquisition costs, and lifetime value to measure growth and profitability in their subscription business.