Insert value Into TableA From TableB Where multiple fields match in both

Hopefully the title sums it up but:

Hello,

I'm working in SQL Server 2008.  

I need to get the value from col1 in Table_A and insert it into col1 in Table_B where Table_A.col2 = Table_B.col2, and TableA.col3 = Table_B.col3, and Table_A.col4 = TableB.col4

The relationship is one to many Table_A to Table_B.

Hopefully that makes enough sense.  

Thanks in advance!!!