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So far every macro has needed a button or Alt+F8. Events are macros Excel runs for you when something happens: the file opens, a cell changes, the user switches sheet, the file is about to be saved. They’re how you build workbooks that feel like small applications — status columns that stamp the time when updated, codes that turn uppercase as you type, warnings before saving an incomplete sheet.

Where event code lives

Not in a normal module. Event code goes in the module of the object that raises the event:

• Sheet events — double-click the sheet (e.g. Sheet1 (Tasks)) in the VBA Project window.
• Workbook events — double-click ThisWorkbook.

At the top of that code window, pick the object in the left drop-down (Worksheet or Workbook) and the event in the right one. VBA writes the correct first line for you — use that rather than typing it, because the exact name and arguments matter.

Worksheet_Change: react to edits

A task tracker: when someone changes the Status in column D, write the date and time in column E.

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim c As Range
    If Intersect(Target, Me.Range("D2:D1000")) Is Nothing Then Exit Sub

    Application.EnableEvents = False
    On Error GoTo Done
    For Each c In Intersect(Target, Me.Range("D2:D1000")).Cells
        If c.Value = "" Then
            c.Offset(0, 1).ClearContents
        Else
            c.Offset(0, 1).Value = Now
        End If
    Next c
Done:
    Application.EnableEvents = True
End Sub

Three details make this robust:

• Target is every cell that changed — maybe one, maybe 500 pasted at once. Loop over it instead of assuming one cell.
• Intersect limits the reaction to column D, so editing column A doesn’t stamp anything.
• EnableEvents = False stops our own write to column E from triggering Worksheet_Change again.

Auto-format what people type

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim c As Range
    If Intersect(Target, Me.Columns("B")) Is Nothing Then Exit Sub
    Application.EnableEvents = False
    For Each c In Intersect(Target, Me.Columns("B")).Cells
        If Not IsEmpty(c.Value) Then c.Value = UCase$(Trim$(c.Value))   ' GSTINs and codes in caps
    Next c
    Application.EnableEvents = True
End Sub

A sheet can only have one Worksheet_Change. If you need both behaviours, put both checks inside the same procedure.

SelectionChange: highlight the active row

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    Me.Cells.Interior.ColorIndex = xlNone          ' clears all fill — use on sheets without other colours
    Target.EntireRow.Interior.Color = RGB(255, 247, 214)
End Sub

Handy for wide data, but it wipes existing cell colours. A gentler version uses conditional formatting with a formula that compares ROW() to a cell the macro updates.

Workbook events

' In ThisWorkbook
Private Sub Workbook_Open()
    Worksheets("Dashboard").Activate
    Worksheets("Dashboard").Range("B1").Value = "Opened " & Format(Now, "dd-mmm-yyyy hh:nn")
End Sub

Private Sub Workbook_BeforeSave(ByVal SaveAsUI As Boolean, Cancel As Boolean)
    If Application.WorksheetFunction.CountBlank(Worksheets("Invoice").Range("B3:B8")) > 0 Then
        MsgBox "Fill in all invoice details (B3:B8) before saving.", vbExclamation
        Cancel = True                                ' stop the save
    End If
End Sub

Setting Cancel = True in a “Before” event stops the action. The same works in BeforeClose, BeforePrint and Worksheet_BeforeDoubleClick.

Useful events at a glance

Where people go wrong

• Nothing happens: code is in a normal module, the procedure name is misspelt, or macros/events are disabled (EnableEvents left off).
• Excel freezes: the event changes a cell, which fires the event again, forever. Use EnableEvents = False.
• Undo stops working: any macro that changes cells clears Excel’s undo history. Mention this to users of event-driven sheets.
• Formulas don’t fire Worksheet_Change: recalculated values don’t count as changes. Use Worksheet_Calculate for that.

Practice

The workbook has a task tracker with automatic timestamps, a codes column that converts to uppercase, double-click tick boxes and a BeforeSave check. Open the code behind each sheet to see where everything lives.

Next: UserForms — your own data-entry windows with dropdowns, validation and buttons.