Refer to another module

I have a small problem with a macro. I have two different moduls in my code. 
In module1 i have the code for some buttons and so and in module2 i have the 
code for what happens if i press the buttons. However my code has trouble 
finding the different modules and I need help on how to write this properly. 
Code in module1:

Sub Create_Menu()
Dim MyBar As CommandBar
Dim MyPopup As CommandBarPopup
Dim button1 As CommandBarButton
.....
Set button1 = .Controls.Add(Type:=msoControlButton)
With button1
  .Caption = "Button!"
.BeginGroup = True
 .OnAction = "button1_Click"

and in modul2:

Sub button1_Click()
Dim objChart As ChartObject


Now I need help with how to refer to the sub. My code is quite messy if i 
have to have it in the same module so it would be prefect it that was 
possible. Thanks very much in advance!