In 2005 and 2006 the Australian Government asked the Ombudsman to investigate 247 immigration detention cases. Eight published reports contain the results of those investigations. The purpose of this new report is to draw together ten lessons from the referred immigration reports that are relevant to all areas of government. The administrative problems and errors exposed in those reports are not unique to immigration administration. The experience of the Ombudsman’s office, gleaned from thirty years of administrative investigation, is that similar practical problems recur in all areas of decision making. Agencies should heed those lessons to guard against administrative error and ensure good decision making. While this report draws many examples from the referred immigration reports, the purpose in doing so is not to direct any further criticism at immigration administration. The Department of Immigration and Citizenship gave its full cooperation and support to these investigations and has worked hard since 2005 to address the weaknesses that were identified.