Rinse the potatoes thoroughly and chop into bite sized pieces. Bring a large pot of water to a rolling boil. Place diced potatoes into the boiling water and cook for 10 minutes or until fork tender.
Use a colander to drain the water off the cooked potatoes and rinse with cold water to cool slightly. Place the cooked potatoes into a large bowl.
Add the diced celery, mustard, lemon juice, vinegar, olive oil, parsley, oregano, salt, and pepper to the bowl. Mix thoroughly until everything is evenly distributed.
Cover bowl and chill for at least an hour before enjoying. Keep leftovers refrigerated in an airtight container or bowl for up to a week.