SAS 70 is an acronym for Statement on Auditing Standard 70; it was developed and is maintained by the AICPA (American Institute of Certified Public Accountants). Specifically, SAS70 is a “Report on the Processing of Transactions by Service Organizations. SAS 70 provides guidance on the factors an independent auditor should consider when auditing the financial statements of an entity that uses a service organization to process certain transactions. It also provides guidance for independent auditors who issue reports on the processing of transactions by a service organization for use by other auditors.

SAS 70 Wiki