Need A Formula To Display Sum If Matches (Array, Sumproduct?)

I have a workbook with two sheets:

Sheet1!A:A contains unique text string values
Sheet2!A:A contains multiple instances of Sheet1!A:A values
Sheet2!B:B contains number values

In Sheet1!B2, I would like to use a formula that would display the sum of the number values from Sheet2!B:B in the rows where Sheet1!A2 matches Sheet2!A:A.

Thanks!

Try =SUMIF

=SUMPRODUCT did not work for me, but =SUMIF did the trick! Thanks a lot!!!