Do Catholics pray to saints?
Short answer: no. We ask them to pray with us. Worship belongs to God alone.
It is a fair question, and it deserves a plain answer rather than a defensive one. On this site you will find prayers that address Our Lady, Saint Michael, Saint Francis, Saint Clare. If that looks like worship being handed to someone other than God, here is exactly what is meant by it.
The distinction the Church actually draws. There is a word for the adoration owed to God, and it is owed to God alone: latria. It is never given to any creature, however holy — not to Mary, not to an archangel, not to any saint. What is offered to the saints is dulia, honour, the same kind of thing in kind (though not in degree) as the respect you show a good person you admire. Mary receives more of that honour than anyone else, and the Church calls it hyperdulia — but it is still honour, not adoration. The difference is not one of degree. It is a difference of kind.
What "pray" actually means here. The English word has narrowed. For most of its life it simply meant to ask — as in "I pray you, sir," which is how Shakespeare uses it and how a courtroom still uses it. To pray to a saint, in the old and proper sense, is to ask a saint — nothing more. Read our prayers and you will see the grammar is consistent: pray for us. Ask for us. Intercede for us. They are requests for someone to pray alongside you, addressed to a friend, not petitions for salvation addressed to a god.
The one Mediator. Scripture says there is one mediator between God and men, the man Christ Jesus (1 Timothy 2:5), and Catholics believe that without reservation. No saint is a second mediator, an alternative route, or a way around Christ. But notice what Paul writes three verses earlier, in the same breath: he urges that supplications and intercessions be made for everyone. Asking others to pray for you does not compete with Christ's mediation — Paul commands it in the very passage that establishes it. Every saint's prayer reaches the Father the same way yours does: through Christ, and only through Christ.
Why ask the dead? The premise of the objection is that they are dead. The Christian claim is that they are not: God is not the God of the dead but of the living (Matthew 22:32). If you would ask a praying friend across the street to remember you, there is no reason the request becomes illegitimate because the friend has finished the race. Scripture shows those in heaven aware of us and holding our prayers before God — the elders in Revelation offer golden bowls of incense, "which are the prayers of the saints" (Revelation 5:8), and an angel offers incense with those prayers at the altar (Revelation 8:3–4). "The prayer of a righteous man has great power" (James 5:16); the saints are simply the righteous who have arrived.
The plainest test. Ask what is being requested. Catholics do not ask a saint to forgive sins, to save a soul, or to be adored — those belong to God, and to ask them of anyone else would be idolatry, and the Church has always said so. What Catholics ask is what you would ask your grandmother: pray for me.
Catechism of the Catholic Church 956, 2683; Lumen Gentium 49–50.