Hello, I'd like to request a feature that would tremendously help (my) users to use workflows and galaxy in general: The ability to specify fixed datasets as input to workflows. Here's a use case: I have a big workflow, with several input datasets (see attached image 1). The shown workflow is just an example, but it illustrates the point: The first dataset is the "real" input - a FASTQ file that will change every time I use the workflow. The other two input datasets are always the same (or more precisely: when the user will run the workflow, he/she should always choose the same datasets - two interval files, representing exons and UTRs, for example). A real world workflow can have many many more 'fixed' datasets, used at different steps of the workflow. If I have six FASTQ libraries and I need to run the same workflow on all of them - I need to select each time the proper input datasets. This is annoying and time consuming (minor problems), and very error prone (major problem). If I want to be well organized and use a different history for each FASTQ library - copying the input datasets between histories is also a bit frustrating. What I wish I had is a way to tell an input dataset in a workflow to always use a fixed dataset - selectable at the time I edit the workflow (see attached image 2 for a mock-up UI). When the use clicks on the "Select Dataset" button, he will be shown a the list of histories, then he will select a history, then he will be shown the list of datasets in that history, and the he will select the fixed dataset. When he runs the workflow, that specific input dataset will be 'locked' and will says something like: "Using dataset NAME from history NAME". I'd be glad to provide more details and use cases, if needed. Thanks for reading so far, -gordon