Clients tell us that software-as-a-service (SaaS) vendors are too numerous (and too small) for a formal sourcing process to apply in all cases. At the same time, the business-led, ungoverned model of "shadow" SaaS deployment has proven problematic — for cost, technology architecture, and security. SaaS marketplaces such as Salesforce AppExchange can alleviate this burden. This report helps application development and delivery (AD&D) pros use marketplaces to succeed with sourcing and governing the proliferating landscape of SaaS vendors. This report replaces our 2017 research on SaaS marketplaces.