Hi Christoffer, This is because those tasks were introduced with IDL 8.4.1 and ENVI 5.2.1. You can usually see this at the bottom of each documentation page under the Version History section. For the ImageToImageRegistration task (http://www.exelisvis.com/docs/ENVIIma...) this was introduced for ENVI 5.2 Service Pack(SP) 1, which means ENVI 5.2.1. You will need to upgrade to get access to these tasks, which are continuously being added to each release of ENVI. To see all of the tasks that were added to ENVI 5.2.1 you can look at the following web page: http://www.exelisvis.com/Learn/CaseSt... I should also point out that ENVI 5.3 and IDL 8.5 will be released in a couple of months, so I would keep an eye out for that upgrade as well.