How do you Concatenate in Report Expressions

Question

How do I concatenate in the expression builder.  I have a report and in there is an expression textbox.  I can get it to display dataset info no problem.  I can even get it to concatenate an expression and then a string  =(expression + "string") But I cannot figure out how to concatenate multiple expressions together.  

I thought this concept would work, but it fails every time  

=Sum(Fields!PV_EXAMINER.Value, "DataSet2") + " " + User!Language