Use 2 data sets in one chart in SSRS

This may not work for all types of charts, and does require your datasets to be constructed with common axis values:

• Select the chart so that the "chart data" panel appears.

• Click the green "+" above the "Values" pane. You'll see a list of fields in the dataset bound to the charts data region. Rather than choosing any of those, choose "Expression" on the very bottom.

• Add a value from your other dataset - note that it will probably need to be wrapped in an aggregate function, like SUM or FIRST. For example:

  =sum(Fields!YourField.Value, "2ndDatasetName")

• All datasets will need to have common axis values, otherwise you're in for a bad time. If you need to split them up, you can have TWO sets of axis values for each orientation (vertical, horizontal); to change which axis position is used, bring up the "Series Properties", choose the 2nd tab on the left ("Axes and Chart Area"), and choose the Primary or Secondary axis accordingly.