OBJECTIVES: Our objective was to assess whether 15 Key Principles, previously proposed by our group -- the International Working Group for HTA Advancement -- could be applied to health technology assessment (HTA) programs in different jurisdictions and across a range of organizations and perspectives. METHODS: We investigated the extent to which 14 HTA organizations around the world implicitly support and implement the Key Principles.  By “support,” we meant that the organization backs the principle in written guidelines or other form, regardless of whether they actually follow it.  By “implemented,” we meant that published reports and decisions based on reports were consistent with the principles.  The HTA organizations were chosen to include examples of both established and emerging entities with different roles and objectives.  They include HTA organizations in Australia (PBAC), Brazil (ANVISA), Canada (CADTH), Germany (DAHTA@DIMDI, IQWiG), Korea (HIRA), Sweden (TLV, SBU), Taiwan (CDE), the United Kingdom (NICE), and United States (Blue Cross/Blue Shield, CMS, DERP, Wellpoint). RESULTS: There is considerable variation in practices across the HTA organizations.  Many of the organizations support and implement certain principles, such as being explicit about their HTA goals and scope; considering a wide range of evidence and outcomes; and seeking all available data.  Other principles, such as taking a full societal perspective; having a clear system for setting priorities; explicitly characterizing uncertainty surrounding estimates; monitoring the implementation of HTA findings; and considering the generalizability and transferability of results receive much less backing.  There is also variation in the degree to which organizations incorporate appropriate methods for assessing costs and benefits.  CONCLUSIONS: There is considerable room for improvement for HTA organizations to adopt principles identified to reflect good HTA practices.  A broader discussion is needed on principles that do not receive widespread support and implementation.