How to get values from Child window to parent window

Sometimes we have a simple problem and we think its really very complex and leave it. But listen its wrong attitude. We have to solve each and every problem which are comming in our life. I face a problem that I was unable to get the values from child(Popup) window to parent window. what we need to do for setting values from child window(PopUp window/Dialog) to parent window's control(textbox). Just required to add the following javascript where we required to add the values from child to parent windows control.

I am here inserting a value in parent windows TextBox named txtTo from my child windows(PopUp dialog's) TextBox values.

Dim strScript As String = ""
Response.Write(strScript)

This will get the value of txtPopUpTitle textbox and set it in the txtTo.

Regards,
Vijay Modi