These books were written by the Apostle Paul, one of the earliest missionaries to take the Good News about Jesus to non-Jewish people. They are commonly referred to as Epistles, because they were written as letters to churches or individuals with whom the Apostle was familiar or hoped to visit.
Romans
1 Corinthians
2 Corinthians
Galatians
Ephesians
Philippians
Colossians
1 Thessalonians
2 Thessalonians
1 Timothy
2 Timothy
Titus
Hebrews