Olympiacos F.C., also known as Olympiacos C.F.P. (Greek: Ολυμπιακός Σύνδεσμος Φιλάθλων Πειραιώς - Ο.Σ.Φ.Π. - Olympiacos Syndesmos Filathlon Pireos), Olympiacos Club of Fans of Piraeus, is a Greek association football club, part of Olympiacos CFP, based in Piraeus, Athens.

Olympiacos is considered one of the big three football clubs in Greece and it is one of the only four teams that have never been relegated from the first division. Olympiacos are by far the most successful club in Greece, having won the Greek League 35 times, the Greek Cup 22 times, 3 Greek Super Cups and 1 Balkans Cup, more titles than any other Greek team. Olympiacos is also one of the founding members of the European Club Association.