Fast answer
To merge two lists without duplicates, paste the first list into List A, paste the second list into List B, choose Union, and copy the output. Union keeps every unique item from both lists and removes repeated lines automatically.
If you want to stack both lists first and then deduplicate, choose Concatenate and turn on Remove duplicates. That keeps the first occurrence of each item and is often the best choice when the original order matters. For the fastest version, open the Merge Lists tool and paste both sources directly.
Example: merge two email lists
Imagine you exported one email list from a newsletter tool and another from a signup form. Some people appear in both. The goal is one clean master list with every address only once.
In this example, [email protected] and [email protected] appeared in both lists. Union includes them once, then adds the unique addresses from each source.
Which merge mode should you use?
Union
Best default for “merge two lists without duplicates.”
Use this for email lists, keyword lists, tag lists, domain lists, customer IDs, and any task where the final output should contain each item once.
Concatenate + Remove duplicates
Best when you care about preserving the first list’s order.
This stacks List B after List A, then removes repeats. If an item appears in both, the List A version wins because it appeared first.
Intersection
Best when you only want overlap.
This does not create a master list. It shows only the items that exist in both lists, which is useful for finding shared subscribers, duplicated records, or common keywords.
Interleave
Best when the order should alternate between two sources.
This is useful for schedules, playlist ordering, quiz questions, or assignment rotation. It is usually not the right choice for deduplication unless you also enable Remove duplicates.
Merging lists from Excel or Google Sheets
- Copy the first spreadsheet column and paste it into List A.
- Copy the second column, another sheet export, or another CSV preview and paste it into List B.
- Choose Union if you want every unique row, or Concatenate plus Remove duplicates if you want List A order to stay first.
- Turn on Sort result A-Z only if alphabetical output matters more than original order.
- Copy the merged output and paste it back into your spreadsheet, CRM, email tool, or notes.
Tip: copy one column at a time. If you paste multiple spreadsheet columns, the tabs may stay inside each line, which can be useful for some workflows but confusing if you expected a simple one-item-per-line list.
Case sensitivity and whitespace
Most deduplication should be case-insensitive. That means Apple, apple, and APPLE are treated as the same item after trimming whitespace. This is usually correct for names, emails, domains, tags, and keywords.
Turn on case-sensitive matching only when capitalization changes the meaning, such as product SKUs, code identifiers, acronyms, or datasets where us and US should not be merged.