Just to summarize what I found about getting tool parameter <param type="library_data" > going again (though a future expansion of dataset parameters to handle this would be great, esp. if one can specify a particular data library): 1) Aysam's patch (thanks!) 2) Tool_form.mako has a hardcoded url that doesn't work for galaxy installs that have a prefix so that needs adjustment: $(".add-librarydataset").click(function() { var link = $(this); $.ajax({ url: "/visualization/list_libraries", Now one gets the popup form in one's tool where one or more library datasets can be selected. Selecting one or more gets them listed in one's tool form. However, I'm not understanding how to get those items submitted with galaxy form <command> params. I tried for example: -B "$library_datasets[0].file_name" and also tried a loop to enumerate the dataset file names. I keep on getting: File "cheetah_DynamicallyCompiledCheetahTemplate_1421706558_2_37415.py", line 203, in respond TypeError: object of type 'LibraryDatasetValueWrapper' has no len() If anyone knows the solution, that would be appreciated. Damion Hsiao lab, BC Public Health Microbiology & Reference Laboratory, BC Centre for Disease Control 655 West 12th Avenue, Vancouver, British Columbia, V5Z 4R4 Canada