So I have a Workbook_open sub that creates Long variables when workbook is opened:
Private Sub Workbook_open() MsgBox ("Workbook opened") Dim i As Long i = 68 End Sub How would I pass the i value to a Worksheet_change sub for a particular worksheet?
Dim i inside a procedure scope makes i a local variable; it's only accessible from within the procedure it's declared in.
The idea of passing i to another procedure is very sound: it means you intend to keep variable scopes as tight as possible, and that's a very very good thing.
But in this case it's too tight, because the parameters of an event handler are provided by the event source: you need to "promote" that local variable up one scope level.
And the next tightest scope level is module scope.
You can use the Dim keyword at module level, but for consistency's sake I'd recommend using the keyword Private instead. So in the same module, declare your module-level variable:
Option Explicit Private i As Long Private Sub Workbook_open() MsgBox "Workbook opened" i = 68 End Sub If you want to expose that variable's value beyond this module, you can expose an accessor for it:
Option Explicit Private i As Long Private Sub Workbook_open() MsgBox "Workbook opened" i = 68 End Sub Public Property Get MyValue() As Long 'invoked when MyValue is on the right-hand side expression of an assignment, 'e.g. foo = ThisWorkbook.MyValue MyValue = i End Property Now the Sheet1 module's Worksheet_Change handler can read it:
Private Sub Worksheet_Change(ByVal Target As Range) MsgBox ThisWorkbook.MyValue End sub But it can't write to it, because the property is "get-only". If everyone everywhere needs to be able to read/write to it, then you might as well make it a global variable, or expose a mutator for it:
Option Explicit Private i As Long Private Sub Workbook_open() MsgBox "Workbook opened" i = 68 End Sub Public Property Get MyValue() As Long 'invoked when MyValue is on the right-hand side expression of an assignment, 'e.g. foo = ThisWorkbook.MyValue MyValue = i End Property Public Property Let MyValue(ByVal value As Long) 'invoked when MyValue is on the left-hand side of an assignment, 'e.g. ThisWorkbook.MyValue = 42; the 'value' parameter is the result of the RHS expression i = value End Property 
Property Set and Property Let both exist (where Property Set is a mutator for an encapsulated object reference), and "letter" just doesn't quite cut it ;-)ThisWorkbook members to set/let and get. I guess the code above is to reside in ThisWorkbook code pane, isn't it?ThisWorkbook is just a special kind of a class module - it's a document module which inherits all members of the Workbook class, and has a VB_PredeclaredId attribute (like a UserForm module) which makes its default instance globally accessible - so depending on whether you're referring to the type or the object, ThisWorkbook is either the module itself, or the default instance of that class, respectively.For that, declare i as a Public Variable on a Standard Module like Module1 and then you can access the value of i in Sheet Change Event if it is initialized during Workbook Open Event.
On Standard Module:
Public i As Long On ThisWorkbook Module:
Private Sub Workbook_open() MsgBox ("Workbook opened") i = 68 End Sub 
i means and which one is being referenced (since everybody likes using i for loop indexes and other random, obscure purposes).i is just OP's MCVE - I don't think anyone would make a global variable actually named i =)
Worksheet_changeinstead?