Selective regression testing involves retesting of software systems with a subset of the test suite to verify that modifications have not adversely impacted existing functions. Although this problem has been heavily researched, it has never been discussed in the context of SaaS (Software as a service). This paper presents the specific requirements, challenges and benefits in delivering regression test selection as a service (RTaaS). We will introduce how to design and implement a RTaaS platform. An implementation of RTaaS has been piloted and improved via several real projects in China market. The real customer cases help illustrate that RTaaS is a cost-effective and easy way for software project teams to leap over technical barriers and tap into advanced regression testing selection technologies. © 2011 IEEE.