Or another way (found on another forum - apologies to the author; you know who you are :))
=IIf(IsNull([Address1]),"",[Address1] & ", " & IIf(IsNull([Address2]),"",[Address2] & ", " & Chr(13) & Chr(10)) & IIf(IsNull([Address3]),"",[Address3] & "," & Chr(13) & Chr(10)) &...