Question: How do I  merge three columns into one list?

Answer:

Excel 2007 array formula in D2:

=IFERROR(INDEX(List1, ROWS(D1:$D$1)), IFERROR(INDEX(List2, ROWS(D1:$D$1)-ROWS(List1)), IFERROR(INDEX(List3, ROWS(D1:$D$1)-ROWS(List1)-ROWS(List2)), ""))) + CTRL + SHIFT + ENTER copied down to D13.

Named ranges
List1 (A2:A6)
List2 (B2:B3)
List3 (C2:C5)

What is named ranges?

How to implement array formula to your workbook
Change named ranges. If your merged list starts at, for example, F3. Change D1:$D$1 in the above formula to F2:$F$2.

Download excel sample file for this tutorial.
merge-three-columns.xlsx
(Excel 2007 Workbook *.xlsx)

Functions in this article:

INDEX(array,row_num,[column_num])
Returns a value or reference of the cell at the intersection of a particular row and column, in a given range

ROWS(array) returns the number of rows in a reference or an array

IFERROR(value;value_if_error) Returns value_if_error if expression is an error and the value of the expression itself otherwise

Related posts:

1. Merge two columns with possible blank cells in excel (formula)
2. Count matching cell values in two columns in excel