Object variables (ranges, worksheets, workbooks, dictionaries) must be assigned with Set. Values (numbers, text, dates) are assigned with a plain equals sign.

Code

Dim ws As Worksheet
Set ws = Worksheets("Data")

• A sheet variable

  Dim ws As Worksheet Set ws = Worksheets("Data") → ws now refers to the sheet

  Then ws.Range("A1") and so on.

• A range variable

  Dim rng As Range Set rng = ws.Range("A1").CurrentRegion → A range variable

  Reuse without retyping the address.

• Release

  Set ws = Nothing → Releases the reference

  Optional at the end of a procedure.

• Forgetting Set gives "Object variable not set" (error 91).
• Forgetting Set gives runtime error 91, "Object variable or With block variable not set".
• If rng Is Nothing tests whether an object was assigned.
• Set works with any object, including Application.

• Writing rng = Range("A1") without Set assigns the value, not the range.
• Comparing objects uses Is, not =.